There is a problem were the Severity on UIM associated alarms as well as the Cleared On/By information is missing in the Events table of the relevant models.
Release : 20.2
Component : Spectrum Alarm & Event Management
Check and make sure that your system is logging event 0x10706:
0x10706: User {u} cleared alarm number {I 0x0700} with probable cause id {H 3} for device {m} of type {t}
If that's disabled, then you will not see the clear in the Event Tab.
Also check the clearing event 0x10702 in the Event Configuration and make sure that it is being stored to the Archive Manager DB (DDMdb) along with 0x10701