Hi @Adhost, Thank you for taking the time to reply. This is very much appreciated. Deactivating OWASP_CRS/ATTACK-GENERIC resolved the issue. I can now log into my Umbraco websites!
Hi @Adhost, Plesk 18.0.70 update #2 has just been installed on our server and all 4 Umbraco websites are experiencing same issue (we use 2 completely different versions of Umbraco also). Did you manage to find a solution to this please?