All issues listed below are issues with DRM that have proven to be endemic or are ones that I know of but cannot fix. This will be updated as needed.

KNOWN ISSUES

1) Only Irregulars and Nobles are Spawning
This is because your installation of ATC failed or you have loaded it after DRM. If you are only seeing the [Culture] Fighter units and noble recruits, then try reinstalling the latest version of ATC and make sure that it is loaded prior to DRM.
Remember that not every settlement will have the alternative units due to the roll of the dice or the AI getting to them first, so I would recommend sampling a bunch of settlements before drawing conclusions.
Be aware that if working on an existing save, ATC only affects new units, so use a new campaign if you want to see if ATC is now working correctly.
Additionally, Tevea has some weird scripts around it so it might put in some Calradian Fighters even if ATC is working correctly. I would not use Tevea as a sample settlement when testing.

2) Tier 1 Recruits Not Spawning
This is an ATC issue - Adonnay has a setting that was meant to allow you to level up recruits. Unfortunately, it's default setting might increase the tier of units by default. To fix this, open your ATC Configuration and set the "LevelRecruitsUpToTier" value to 0 (or whichever setting you may prefer).

3) [Lord] Needs Troops in [Castle] Crashes!
I have observed this a few times in the past, though I have not seen it recently as of June 2021. This is a TaleWorlds issue, as far as I know, and any potential workaround I might have causes too many issues elsewhere.

4) Customs Battles Does Not Work
Custom Battles has a love-hate relationship with DRM; sometimes it works, sometimes it doesn't. I have no interest in trying to get it to work since it seems to be an issue on the end of Custom Battles, so if you really want to play DRM in a set battle I would recommend downloading the Enhanced Battle Test[www.nexusmods.com]as it has the same purpose but is far more functional.

5) Graphics Benchmark Does Not Work
Similar story to Custom Battles; for whatever reason the game gets mad at DRM being loaded when running the graphics benchmark. Since the benchmark would not include DRM units anyways and even if OSA was added it wouldn't show OSA items, I would just turn DRM off if you need to calibrate your graphics.