The most crippling instance occurred when loading a saved session (a preset, from the menu where one can assign midi CC’s, etc). Like yourself, I am arcless, so that variable is out for my setup. Otherwise, vanilla 128 grid (2019) and vanilla norns (also 2019).
Norns only returned to a normal state after I pulled the plug via the kill switch on the bottom.
FWIW, this has only happened 2-3 times, out of probably 30 sessions.
Part of the difficulty here is that, when this flavor of lockup occurs, maiden/matron don’t produce a readout. Is there any kind of log file that one can pull after the fact? Sorry for my ignorance, I’m trying to be helpful, but alas am a level three minstrel.