Ok not sure what the error was but it seems to work now. I formated the SD and unpacked the files from the Git into it. Then I installed the update to 3.1.1 again an uploaded a fresh firmware from the fw generator. No idea what went wrong before.
reprap.htm.gz is not present in Duet2and3Firmware-3.1.1.zip so if you used it previously with 3.1.1 i'd put my $ on reprap.htm being leftovers after upgrades.
you could perhaps try install older dwc and then upgrade to 3.1.1 again to see if it remains functional, but i wouldn't be surprised if it broke sooner or later.
