Does not work in incognito.
Unfortunately I cannot provide access to the server, but I can provide more details from ssh.
Also, is it possible to roll back to Plesk 17 until the newer version becomes more stable?
Plesk stopped working after upgrading to 18.0.20. It just shows a plain link on white screen labeled "web admin edition" which points to "https://mydomain.com:8443/smb/web/view" and infinitely loops within URL...