Possible 3.6 RC3 error

[DuetUser]

We run 14 (MB6HC) machines on 3.5RC3 firmware, for months, without problems, we do not ever turn them off.
I updated 2 of them to 3.6 RC3.
After hours of idle, I tried to print something and noticed that one of the motors (a co extruder connected to MB6HC driver) vibrates instead of extruding.
I restarted the machine and the problem went away.
The second one was merrily printing until in a random moment a Z motor started to vibrate (like phases being messed up) instead of moving the bed up and down. This was a serious thing, which could easily lead to a disaster.
Again after a restart, everything went back to normal.

Both machines were operating correctly on 3.5RC3 for a long time.

[dc42]

@DuetUser if a motor vibrates instead of moving, that usually means that only one of the phases is being energised. Possible reasons include:

1. Bad connection between the motor and the Duet
2. Driver has detected a short circuit on one of the outputs and has shut off the driver
3. Failing solder joint on the Duet

In cases 1 and 2 the Drivers section of the M122 report should report the error. So if it happens again, run M122 before restarting.

[DuetUser]

@dc42 There was no info like "Phase A short to ground" on Panel Due, usually there is.
We've never experienced such problems not related to hardware issues you describe, on 3.5RC firmware.
I know them well because they occur when reconnecting extruder motors to the toolboard and damaging wires / pins.
We roll back to 3.5 RC3 and see what happens.

[dc42]

@DuetUser gave you tried firmware 3.5.4 ?