What if you use it against specific file system and not All (as intended originally by developers)?  So, try to create separate group with client doing only dense fs and using PSS and see if that breaks.

I already did it (client config  wih save set /abcde, with directive and without directive) and I have problem to make initial full backup with PSS.

I did upgrade of NetWorker on client to version 8.2.1.6, but problem still persist ...

Best thing is to run backup in debug mode then and if that doesn't give clue just give it to support.

support is already working on it, but no progress...