Symptoms

Loads of the errors similar to this one being logged in host server log:

64007 Provider did not return a result for K2:DOMAINUSER on GetUser

All error messages mention users who already disabled in AD and seemingly they also have Enabled flag set to 0 in K2 Identity.Identity table.
 

Diagnoses

There is a known issue (internal ID 607716) in pre-4.7 versions of K2 (4.6.9/10/11). In these versions Identity Service/ADUM enables disabled users again whenever it tries to resolve any group disabled user belongs to. As this user disabled in AD, subsequent identity cache update call for user information causes error being logged and user becomes disabled once again.

In large scale AD DS environments this can easily cause excessive logging and removing disabled users from all groups used in K2 is not always an option.

Resolution

This issue has been fixed in 4.7 release OOB and there is also a coldfix addressing this problem in 4.6.10/11 available upon request to K2 support.

Potential workaround for this issue may also be removing disabled users from all groups used in K2.