@dc42 the answers were able to resolve the problem, thanks everyone for the help!

@gloomyandy here you go: m122-homing-problem.txt

sorry for the late response, I'm only infreqently near the machine atm

We are using a e3d toolchanger based printer with a Duet3d 6HC and a 3HC expansion board with web control. All on version 3.5.0beta4. The problem is not present in 3.4.6 (or 3.4.5).

When configuring the z axis endstop to be a z probe and then subsequently run a G1 H1 (or even H4) we observe a reset. Further, after the reset, the expansion board is not detected anymore.

Both the z axis stepper and the probe are connected to the mainboard.

Relevant section of config.g

M558 P5 C"io2.in" K0 H3 F360 T20000
M574 Z1 S2 K0

When we then run z homing we observe reset on the G1 H1 command (tested using the console)

G91
G1 H1 Z-200 F2000

M119 gives expected outputs and detects the z probe state change.

If we define the switch as a regular endstop, z homing functions function. But we require a z probe.

M574 Z1 S1 P"io2.in"

Full config.g and homez.g:
homez.g config.g