Printer stopped midprint, light is turned off, and the followind msg appeared on the screen:
“MCU extra_mcu shutdown: Move queue overflow Once the underlying issue is corrected, use the FIRMWARE_RESTART commandto reset the firmware, reload the config, and restart the host software. Printer is shutdodwn”
There are 2 buttons to be chooosen to continue:
“Network Management” and “Restart firmware”
What happened, what to do now & how to prevent it in the future?
Extra MCU (Micro Controller Unit) is for the tool head.
This can be temperature of the boards, or a wiring thing.
CarDoc likely knows better/more, but also look back over the latest forum posts in the meantime, simlar sounding issues have has popped up multiple times and those users have found a variety of solutions, so one might be the exact same as yours.
I’m not sure if Sovol copy/pasted this issue to the Max (I bet they did)
It seems the problem is solved by deleting gcode remainings. There was 210 MB free disk space only, probably not enough for proper functioning of Klipper.
I had this happen because I had very dense tree supports holding up a large bridge. I lowered the density by making the branches bigger.
No, it’s not solved: it appears even when all the gcode files are deleted except the last one (33.1 MB).
Strange fact: in gcode folder there is 2.2 GB free disk space, but in its subfolder sda1 there is 6.5 GB free disk space. 
How is this possible??
See this thread
Sovol’s (non functional) PLR “method” writes the X, Y, Z, coordinates to a file on EVERY move. Editing one of the python scripts to remove the undocumented hack solves the problem.