I have the same issue. On opening the selectbox for "run as" is empty. When selecting another PHP Version e.g. from 7.0 to 7.1 the logfile (/usr/local/psa/admin/logs/panel.log) shows the following error:
[2017-04-25 09:37:35] ERR [panel] Zugriff verweigert.
I have updated two Servers to...