The legacy build does run on b9s 1.2. If you want to try it, download the latest build labeled "Branch: Legacy" under here:
http://astronautlevel2.github.io/Luma3DS
It's worth a shot, but I'd be surprised if it solved your problem, as it seems very unique and not the typical issues with 8.0/8.1.
I'll take a look at the dumps soon, hopefully - unfortunately, I'm out of town until mid-tomorrow, so I probably won't be able to until then. Until then, here are some things to try:
- Legacy builds (as stated above)
- System format - Make a backup of your NAND with G9M, format your system, and see if it works
- Restoring a previous backup - if you have any backups from before this was happening, try restoring them. (Don't restore if they're a9lh backups - I don't know if they'll work, I'll have to test on a hardmodded system).
That's about all I can think of right now, hopefully something above will work - if not I'll dig into the dumps and see what's happening.