Some of the castle doesn't upgrade until you finish all the quests. That is, little by little as you do quests, upgrades happen. Some of the quests won't start until you have finished the Dawnguard quest "Touching the Sky" (get auriels bow) and Dawnguard's final quest "Kindred Judgement" to (kill Harkon). If you've been using cheat codes to go to areas you shouldn't, you'll step into a trigger box before I thought you should be able to be there, you will undoubtedly destroy the order of the quests, making them broken.

Here is a list of quests on this mod's wiki page. Everything you need to answer your questions should be there.
https://tes-mods.fandom.com/wiki/Castle_Volkihar_Redux#Quests

1st: sounds like you used a teleport cheat (console commands or other cheats) that caused the quests to get set out of order. Triggering quests out of order will destroy the chain of events. If the quests aren't finish-able, you'll never see the castle fully upgrade.

2nd possibility: As far as all those bugs you listed, no one typically runs into all that unless their save is corrupted. Saves are corrupted when you "install mods, make a save, then delete the mods, make a save". When you boot your game the save is still looking for some of the components left by the mods you deleted. This is the #1 cause of all the woes people experience with modded skyrim.

3rd possibility is you did not download all of the mod. Haven't heard of this happening in a while, but it use to on steam at least back in the old days. People would have to re-download this mod several times to get all the files. It is a rather large mod. This can cause textures or objects to go missing. But, only the ones my mod adds.

4th possibility is you are using a light BNB mod. I've heard people say some of those mods don't work well with this mod.

When I built this mod, I made damn sure that none of my mod touches other components of the "Vanilla/Original Game". in other words, I made "copies" of objects or scripts, renamed them, then changed those. The only thing that might be an issue are "switches" that other mods switch on or off that my mod turns on or off. Switches that the game also uses. Switches are enable, or disable scripts that make objects, scenes, quests or NPCs do something/not do something or appear/disappear.

As in the case of my block sunlight hood, it switches off the damage from the sun. Doing so can only be done 1 mod at a time. So if another mod does it, which ever one is at the bottom of the load list, wins as the no sunlight damage switcher. Hope that makes sense.

Those are the only scenarios that I know of that can go wrong. What you are describing I am 99.9% sure is due to the way you managed your mods and used cheats. That is you deleted them when you should only "disable' them. That means your harddrive will always still have any mod you ever installed still on it, but the game "ignores" it. But, if the save needs to reference something out of that mod, it's there and won't break your game.

Your use of cheats to go places before you should have been able to go there will destroy quest chains. Invisible trigger boxes that push the quests forward a step will get triggered early ruining their order.

These invisible quest trigger boxes are "trigger once then self disable". Otherwise, everytime you unknowingly walked through them, you'd push the quest back to that stage.

One more possibility, you have a very antiquated computer that just cant draw all the stuff my mod adds. I do remember one guy 5 years ago that described that problem. We tried everything until he admitted his rig was lacking a good video card and was only a weak ass dual core processor. He had almost no ram either.

Hi ... Wow ... Thanks for the quick reply and support !

I must have missed the fact that progression of the quests upgrade the castle progressively. Is that somewhere in the description? What a great idea. That confirmation helps a lot. I was teleporting blindly just to confirm Redux was installed and working. If the initial external upgrades don't appear, then I fear I have bigger problems.

Re: 2nd: Agree that a corrupted save is always a possibility, especially with the 400+ mods I'm running. I usually try to clean when I start to see problems (starting with saves before the problem occurs). Been modding Skyrim with ENBs since the NMM days and still use it (lol). I follow the mod author's uninstall steps and always start with a clean save, prior to loading a new mod. Always use Loot after each mod install and force load order as needed via the Loot User Meta Data.

I went back and used Skyrim Save Tool to clean the save prior to starting and performed the normal steps (Fix Script Instances, Delete all #, Clean other, Del. Broken Actives, Clean Formlists) to assure the save file was clean of orphan data. Even with that done, the Dawnguard play through issues were still present. Wondering if the DLC install has issues.

Quest progression events keyed off real-time game event triggers are outside of saves. E.g., if entering the main door triggers a welcome dialog and stage script to run and the physical door and enter interaction is missing, then it would be impossible to start that. You would think that coc DLC1VampireCastleGuildhall would put you into the correct place to start it, but the door trigger is bypassed. This bug is a quest breaking event. Why is the castle door missing is a mystery but it has happened enough to get a SE patch ( https://www.nexusmods.com/skyrimspecialedition/mods/36831 ). Mine is the 2nd example.

I am not familiar enough with the way Skyrim quests handle progress within the stages other than the stages themselves. Is setstage to the next stage # game breaking? From all I read, it doesn't seem so unless certain associated stage status is also tracked within Selana's DLC1NPCMentalModel data or elsewhere. If the latter, then all ducks may not be in a row after the bypass, which could also be the problem. Once I got past the Bloodlines hiccup, everything went smoothly till the very end of Touching The Sky (which eventually completed after acquiring Auriel's Bow.

Re: 3rd ... The file I'm using is 129969995-Castle_Volkihar_Redux_a_Player_Home.zip 54.9 MB (57,571,465 bytes) and consists of cleaner_castlevolkihar3.bsa(53,021 KB), cleaner_castlevolkihar3.esp(3,136 KB), previewfile_129969995.jpg(67 KB).

My first thought was that I was missing textures and objects. So it appears to be self-contained inside of the bsa/esp files. I actually downloaded it via steamworkshopdownloader.io to view the contents and be able to load into TES5Edit to view it for debugging purposes. I know, I should be loading it directly from SteamWorkShop and will do so after I get this all working.

Re: 4th ... From the interiors I tested with an older Snapdragon ENB + 0.422 ENBSeries, everything seems to look just fine :-D

Your explanation keeping your mod separate from the "Vanilla/Original Game" and layering functionality affected by load order overrides makes perfect sense. Does that mean that your mod should be close to the very bottom? Currently it is 2E in the load order defaulted by LOOT.

I did the best I could with the Dawnguard showstopper quest bugs I experienced. Most are known bugs with multiple suggested methods to try/combat. The only quest that was inaccessible is the final Kindred Judgment quest. I tried everything to start it including:

Force start Quest (create a Creation Kit patch)
===================================
1. Start Skyrim Creation Kit (ignore all errors)
2. File->Data (select Plugin/Master File (Dawnguard.esm); Check it; Set as Active File; OK (Ignore all errors)
3. Object Window->Character->Quest->DLC1->Main Quest-> Bloodline(2x click to expand window)
4. Check box Start Game Enabled
5. Exit; Save Plugin to patch name (StartBloodlineQuest.esp); Enable it and run Loot on patch

This actually helped with starting the Bloodlines quest along with another suggested fix (related to a conflicting .pex file), but not for Kindred Judgment.

Re: my rig ... it is a customized version of MSI's infinite-x (i7, 1080ti 11GB + extra RAM) from a few years past and can handle just about everything I throw at it.

I haven't run info problems like this till I finally did the Dawnguard play through.

Any ideas on how to fix the castle main door that is missing?

Anyway, thanks for your time and insight.

UPDATE:
Apparently, my install is definitely broke (Redux conditional detection doesn't want to update) since it doesn't have anything displayed in the video after walking over to the boat dock area:

https://www.youtube.com/watch?v=Lzm0LYS5p1w

No new entrances, no new boats, no smithing area, no upgrades at all. Like I mentioned before, all vanilla. Can't progress at all with your quests since the entrance to Master Throne Wing doesn't exist. Shouldn't all that content be present after Redux does the initial upgrade?

Thinking I have a corrupt install ... I uninstalled mod cleanly in NMM (this disabled the esp and removed the 3x files from the Data dir ... verified it). Installed from SteamWorkShop. Checked for 3x files and enabled esp. Reran LOOT.

Loaded Solitude clean save, fast traveled to the Castle, and the spawned upgrade dock area didn't appear.

Checked my Journal Entries for Dawnguard through Touching the Sky and all sub-quest status and optional quests are checked off with the exception of BloodLine (Speak to Harkon) ... where it bugged out at the missing Entrance door event. Even tried resetquest DLC1VQ02 and reset all stages to check the Speak to Harkon (that was missing).

Perhaps the proper faction setting was not logged that may be throwing off Redux's detection logic. It seems like it may require more data than just the Touching the Sky completion flag.

It is strange that the Vanilla Dock area is populated with hostile skeletons(respawned?) like from Chasing Echos even though it was completed and should be cleared or unfriendly vampires/gargoyles attacking.

Also, when I go into the Castle Undercroft entrance and walk around, I do see one of your Dwemer switches inside that turns lights on/off but nothing like in that video.

With both install options behaving the same, then it can't be a corrupt install. This leads me to think that your Redux upgrade conditions aren't being met properly. The question is what am I missing. Do you remember exactly what conditions behind the scenes need to be met for the upgrade to occur?