Using a new SD card seems to have fixed it, I'm not 100% sure though because of the semi-random nature of this problem. Let's say it's resolved for now, if I encounter it again with the new card I'll report it. Thanks for the help in debugging this.

Common ground for 24v and 12v is fine.

I've been away from 3d printing for a while, I've just come back and I tried reproducing this bug again, and it's still there. Although I can't see any additional debug info you're talking about in the M122 output: https://pastebin.com/9GYuUWFF

Phpbb is old and mostly obsolete, use a modern forum engine. My vote is for Discourse.

I have no experience with migrating forums but I have some database experience. If you really want it, it is not impossible to migrate any forum system to any other one, people just don't want to put in the effort to do so or don't have the expertise required.

Shows a 404 error for me.

I think there's something wrong with the link you posted.

Can the 3-piezo under-heatbed setup be directly attached to the silicone heater? And wont the heat damage the piezo speakers? The temperature is quite high, up to 140 degrees.

@Mike:

My PT100 temp sensor is malfunctioning in this beta (1.20b6) - heater fault at 2000 degrees.
It's defined by:
M305 P1 T100000 B4138 C0 R4700 X200

On a side note, has anyone been able to trigger Stallguard yet?

T, B and C parameters have no effect on PT100 sensors, and in the new beta the R parameter configures the reference resistor. If you have the original PT100 daughterboard you should remove the R parameter (and the other parameters I mentioned in case they are used in the future).

It's literally the first result when searching for "duet mounting" on google…

Thanks, will try it and report back.