Für WHMCS 8.3.0 gibt es einen weiteren Hotfix
CORE-17178 - Prevent circular dereference when loading client service list 1.0.0
ZitatAn issue has been identified in the 8.3.0 release - published on 13th October 2021, that can result in high memory usage on the client services page (client and admin side) in when the same Domain value is used more than once.
This could manifest itself as a partially loaded page, or an entry in PHP error logs: