You have installed RM Password Filter and you find the following error in the RM Password Filter log file:

"ERROR, "AddDirectorySecurity","Error Add Directory Security Directory …. \identitysyncservice - System.Secuirty.Principal.IdentityNotMappedException: Some or all identity references could not be translated". 

However, no onscreen errors are displayed during the installation of RM Password Filter.

This is an expected behaviour if you installed RM Password Filter before the RM Unify AD Sync component. It is the RM Unify AD Sync component that creates the identitysyncservice user. 

The correct installation order for RM Unify AD Sync is RM Unify AD Sync, then RM Unify Password Filter. Please install RM Unify AD Sync and reinstall RM Unify Password Filter on the affected server to ensure directory permissions have been applied properly.