Filter server overload issues

Customer: Filter (Client code: 371000013)
SERP Version: 8.5-2019-09-15-1019
Hosting server: WIN Server 2016 Standart
ON: --verbosity=debug-detailed
Log files: ttps://burti.lv/public/custhweinstall/filter_hob.zip

Issue:
Logfile flooded with log text "Already registered". At that time the server is overloaded. CPU 100%
Events like this may happen when users log in. In many cases when "AG" users login:

There are several companies and the user "AG" is in three of them
StandardID
1) andres.grigor@filter.ee
2) andres.grigor@filter.eu
3) andris.griskovs@filter.lv

When looking at the report (Email and Conferences >> report >> Email validation status), the StandardID
andres.grigor@filter.eu is not Validated
but when looking System >> Persons >> Create >> Check Email address - email is Validated

Could the issue be related to the validation process?
Can't repeat on the test server