NullReferenceException in ADS_ADSAccount_Update/(De-)Activate process

Hi all,

facing a problem in One Identity Manager 8.1.5.

We just migrated from OIM 8.1.0 to 8.1.5 and now ADS_ADSAccount_Update/(De-)Activate process always fails with an error at step AdHocProjection.

[1777018] Error executing synchronization project (mycompany.com)'s workflow (Provisioning).
[1777124] Error executing projection step (User) of projection configuration (Provisioning (Provisioning)).
[1777219] Error executing synchronization step (User)!
[1777028] Error loading a system object using its prototype (John Doe)!
[System.NullReferenceException] Object reference not set to an instance of an object.

Note that we use Sync Project to provision changes to AD domain via ARS connector and ARS version is 6.9.

That happens only with user account changes and doesn't happen for other object classes - Contact, OU, Group, etc.

Note also we didn't have that issue before the OIM version upgrade.

Do you have any ideas what is the reason of the issue and how can it be solved?