Fixed by killing the nginx process for the affected user:
root 15970 1 0 2020 ? 00:00:00 nginx: master process (fakeuser.m) -c /var/lib/ondemand-nginx/config/puns/fakeuser.m.conf**
fakeuse+ 15971 15970 0 2020 ? 00:00:00 nginx: worker process
Logging in works fine after a new nginx process is started.
Kind regards.