I resetted the MOX with a medkit file and it worked well!
My admin password is already set, but the first step of setup is unskippable anyways.
There needs to be an exception for this requirement when the PW already exists. Or more specifically, when the medkit was used.
I had the same behaviour quite some time ago.
This is some cache-bug on the web-UI. Try to delete the cache of your browser or use another browser (in my case Firefox didn’t work and I had to temporarily switch to Chrome and it worked as expected).
You can still skip this step by editing the file in
/etc/config/foris
config config 'wizard'
list passed 'password'