Ok, then I must be mistaken (I remember whitelisting our reverse proxy in Fail2Ban, but that must have been on a Linux-machine).
Still very strange: that plesk server resets all requests coming from the reverse proxy and accepts them from all other machines.
None of the existing firewall rules...
Fail2Ban is no longer in the list of components...
Tough it seems to be active: all connections coming from our reverse proxy are refused (In a previous version I whitelisted that IP-address).
Connections from other machines are working.
Same here... Not sure if I can trust the backup for restore (what about the certificates?)...
PS: files are present as '.symlinks', but '...Unable to check existence of the file C:\Program Files (x86)...'