Hehehe so there were a few instabilities in the software, caused by me cheaping out and leeching the 3.3V power from the mainboard. Especially the TFT backlight takes quite a bit and this week I put more SPI flash chips on the flashmultiplexerboard so the screen would freeze now and then.
Nothing a good ol' LM317 can't fix, so after adding a piece of perfboard with a 3.3V regulator dedicated for the TFT and the blackpill, all is fine again.
"Should have put that on the controller board from the start." - Yeah I know *sigh*