After a ton of debugging where nothing made sense, I moved away from using the M200 mainboard and started debugging on a bluepill using...another bluepill. Yes, you can convert a bluepill to a blackmagic probe, and getting that set up was actually key to another project of mine, hacking the obfuscation in Lerdge boards via the PC/SP registers (in essence, while Lerdge has protection set, you can't stop reading the SP/PC registers, so a firmware with the PC counter hacked and SP set to a known value will yield 4 decrypted byte values at a time.

This gave me the chance to take a breath and step away, and when I came back, I synced up, and lo and behold, the mysterious crashes went away. While I can't use the malyan LCD and the serial definition at the same time, it's now at the point where I need to plug a main board into the printer and begin actually testing...