Here is my latest exception log, I left the main comment on the workshop page itself.
That said I did play with a selection of other mods, so likely had some influence (No SBCameraScroll this time though).

https://pastebin.com/02Z1cuVY

I was also playing in coop, and I noticed that sometimes the 2nd player would get teleported to the pipe where we came from, while waiting for a region gate to open (maybe something to do with stick together mod?)

Fascinating. Thank you for bringing this to my attention! The 2nd player is working as intended, but for some reason the first player isn't getting moved. This is what I get for not testing co-op. I should be able to fix this pretty soon.

It should be fixed with version 1.0.2, although I haven't tested it with the Stick Together mod. Apparently the plugin was deleting the room while some players were still in it... problematic. But now it should work! Karma gates should be back to working 80% of the time like in singleplayer.

Thanks for looking into it! Sorry I didn't reply until now, but I really appreciate you fixing it :)

RegionRandomizer: World Loader Error: Object reference not set to an instance of an object
at OverWorld.SyncFloodLevels (AbstractRoom oldWorldRoom, AbstractRoom newWorldRoom) [0x000bb] in <a117a2e773414632b51933d2ae7f2aca>:0
at (wrapper dynamic-method) OverWorld.DMD<OverWorld::WorldLoaded>(OverWorld)
at (wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.Trampoline<OverWorld::WorldLoaded>?-1933393920(OverWorld)
at RegionRandomizer.RegionRandomizer.OverWorld_WorldLoaded (On.OverWorld+orig_WorldLoaded orig, OverWorld self) [0x0005f] in C:\Users\Natha\OneDrive\Nathan\RainWorld Mods\Region Randomizer\RegionRandomizer.cs:731
NullReferenceException: Object reference not set to an instance of an object
OverWorld.SyncFloodLevels (AbstractRoom oldWorldRoom, AbstractRoom newWorldRoom) (at <a117a2e773414632b51933d2ae7f2aca>:0)
(wrapper dynamic-method) OverWorld.DMD<OverWorld::WorldLoaded>(OverWorld)
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.Trampoline<OverWorld::WorldLoaded>?-1933393920(OverWorld)
RegionRandomizer.RegionRandomizer.OverWorld_WorldLoaded (On.OverWorld+orig_WorldLoaded orig, OverWorld self) (at C:/Users/Natha/OneDrive/Nathan/RainWorld Mods/Region Randomizer/RegionRandomizer.cs:712)
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.Hook<OverWorld::WorldLoaded>?599008128(OverWorld)
OverWorld.Update () (at <a117a2e773414632b51933d2ae7f2aca>:0)
RainWorldGame.Update () (at <a117a2e773414632b51933d2ae7f2aca>:0)
MainLoopProcess.RawUpdate (System.Single dt) (at <a117a2e773414632b51933d2ae7f2aca>:0)
(wrapper dynamic-method) RainWorldGame.DMD<RainWorldGame::RawUpdate>(RainWorldGame,single)
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.Trampoline<RainWorldGame::RawUpdate>?1638053888(RainWorldGame,single)
Pom.Pom.RainWorldGameRawUpdate (On.RainWorldGame+orig_RawUpdate orig, RainWorldGame self, System.Single dt) (at C:/Users/ericer/Documents/Rain World Documents/Code Modding/Pom/Pom/Pom.InputHooks.cs:41)
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.Hook<RainWorldGame::RawUpdate>?-1547665408(RainWorldGame,single)
(wrapper dynamic-method) ProcessManager.DMD<ProcessManager::Update>(ProcessManager,single)
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.Trampoline<ProcessManager::Update>?-1244894208(ProcessManager,single)
RegionKit.Modules.AnimatedDecals.VideoManager.ProcessManager_Update (On.ProcessManager+orig_Update orig, ProcessManager self, System.Single deltaTime) (at <5b121b8e5bc846379a4645405d5ae6b8>:0)
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.Hook<ProcessManager::Update>?1137738880(ProcessManager,single)
RainWorld.Update () (at <a117a2e773414632b51933d2ae7f2aca>:0)

Game froze while trying to enter a region gate (going from lush mire to shaded citadel [which went to farm arrays iirc]). Can still pause but the gameplay froze. Playing as Rivulet with two slugpups. Was able to use the gate before I believe.

Mods:
Slugbase, Rain World Remix, Custom Regions Support, Sharpener, POM, More Slugcats Expansion, ExtendedCollectiblesTracker, Expedition, ImprovedCollectiblesTracker, Tokens in Expedition, Rainbow pups, Friends of Friends, X64 World, RegionKit, Faster Remix, Karma Expansion, Howling Rift code stuff, Fisbos, Music Announcements, Slugpup Safari, Lunacy, Let Me Set My Needles Down, THe M4rblelous Entitiy Pack, Lush Mire, Pups for Everyone, Pups+, Purification Conduits, The Grinder, Coral Caves, Region Randomizer, Grinder Patch, Stormy Coast, Badlands, Howling Rift, Arid Barrens, The Mast, Mosquitoes, Gilded Sanctuary, Forsaken Station code stuff, Shrounded Assembly Code, Scorched District, Hanging Gardens, Forsaken Station, Shrouded Assembly, Pilgrims' Ascent, Far Shore, Moss Fields, Chasing Wind, Neuron Forest, Dev Tools, Dev Console, Testing Arenas, IDs Expanded, Visible ID, Forsaken Factory, Merge Fix, No Mod Thumbnails, Input Display, Dress My Slugcat

also idk who nathan is

@funkypistachios, this is a Rain World error not necessarily related to my mod. I believe it happens when it is unable to find a gate to link up to. 80% of the time (in my experience), this is due to lacking a region mod that you had when you first started the randomizer for Rivulet but has since been disabled. (I had a near-identical issue once: the randomizer was looking for GATE_RA_LF in Farm Arrays, but I had accidentally disabled Radiosphere, so I got the same issue).

So... there's a chance Rain World just bugged, in which case maybe it'll work if you try it repeatedly. Or maybe a region mod got disabled accidentally. Most likely, other gates should still work, though.

Thanks for the detailed bug report. I'll try to update the error logging to make it more helpful for me next time.

IndexOutOfRangeException: Index was outside the bounds of the array.
Menu.EndgameMeter+NotchMeter..ctor (Menu.EndgameMeter owner) (at <a117a2e773414632b51933d2ae7f2aca>:0)
Menu.EndgameMeter..ctor (Menu.Menu menu, Menu.MenuObject owner, UnityEngine.Vector2 pos, WinState+EndgameTracker tracker, FContainer bkgContainer, FContainer mainContainer) (at <a117a2e773414632b51933d2ae7f2aca>:0)
Menu.KarmaLadder..ctor (Menu.Menu menu, Menu.MenuObject owner, UnityEngine.Vector2 pos, HUD.HUD hud, RWCustom.IntVector2 displayKarma, System.Boolean reinforced) (at <a117a2e773414632b51933d2ae7f2aca>:0)
Menu.KarmaLadderScreen.GetDataFromGame (Menu.KarmaLadderScreen+SleepDeathScreenDataPackage package) (at <a117a2e773414632b51933d2ae7f2aca>:0)

Was playing Pearlcat with Simple Spawn Swapper on. Sheltered and this happened.

@WorldCreator67 this has almost certainly no relation to the Region Randomizer mod. None of these methods are affected by Region Randomizer. If you're playing with my Karma Expansion mod, that MAY be the problem; however, still: None of the mod's methods are in the error log. So it is most likely an issue with Pearlcat being hardcoded to only support 10 karma??

@TheLazyCowboy1 I do not have Karma Expansion on. Also want to mention that the game seems to kick me out of the karma gate the second it starts closing and accelerates the game for the next room as well.

@WorldCreator67 okay, so the game acceleration may be the problem. Forceably removing all creatures from the gate is intended behavior (it took me many hours to get it to work), because otherwise the gates might not link up properly. However, the game acceleration... does it apply to most gates you use, or only some? Could you send me a more comprehensive mod list? Does re-entering the gate and then leaving fix the problem, or does that cause the game to crash? (If it does cause the game to break, awesome! Send me the error logs if it does that.)

This MIGHT be the issue causing sheltering to glitch. This was a very common bug in previous versions of the mod, but I haven't experienced it at all since my latest patch.

@TheLazyCowboy1 sorry for the late reply, the acceleration only happens for the room after the game (it also effects fall damage, making the VS-SI pole fatal if you fall from it) So far it's occurred with every gate I've used, but idk what could be causing it.

@WorldCreator67 I appreciate you reporting the issue. Obviously you have no obligation whatsoever to help me, but I would really appreciate 3 things from you: 1. Would you send me the contents of the file "C:\Program Files (x86)\Steam\steamapps\workshop\content\312520\3309195090\world\RegionRandomizerModList.txt" if it exists? (It it doesn't exist, that's fine). This will give me your full mod list at the time of last randomizing the world, so I can make sure no other mods are interfering. 2. Does re-entering and leaving the gate fix the issue? 3. Are you playing on multiplayer or with slugpups?

...I really want to get this issue fixed, because it really annoys me...

@TheLazyCowboy1 TERRIBLY SORRY FOR NOT REPLYING EARLIER, I suck at keeping track of steam discussions, but yeah I can try to recreate my conditions

So I tried to recreate the issue and it didn't happen again. No idea what happened, but I'm thinking it might've been a memory issue?