- Unable to access Plesk UI or some websites, it keeps loading endlessly.
- There are no errors at Domains > example.com > Logs page, in
%plesk_dir%adminlogsphp_error.logfile or in the Event Viewer.
- Reconfiguration of PleskControlPanel website in IIS does not help.
IIS web-server does not handle requests properly.
Note: IIS restart will make all the websites offline for a while, consider doing it in maintenance time.