Symptoms- Plesk is not login to Plesk UI:
TypeError: Cannot read properties of undefined (reading 'toLowerCase') - Log from /var/log/plesk/panel.log shows:
[Action Log] Failed login attempt with login '<invalid>' from IP 203.0.113.2
CauseThe issue is caused by the Kaspersky Antivirus program installed on the PC used to login to Plesk. The
request is intercepted by the antivirus program before being sent, which causes an error.
ResolutionAdd Plesk
URL in the exception list of the Antivirus.