Thank you @NicolasGIS for your quick response.
After enabling administrative access I had trouble accessing services and Server Manager, and discovered the ArcGIS Server Windows service had stopped running. Started it manually but it stopped again after a few minutes. Seemed to work normal after I disabled admin access.
But, as you say, there might have been other issues. Ran into more problems later, for example all data stores failed validation. After troubleshooting for a few hours I finally rebooted the server machine and now everything looks ok.
Will be interesting to see how that bug process evolves. Meanwhile I'll try to enable admin access again and hope my server stays up.
/Anders