Yes!
The problem occurs on and off.
Restarting the shield does not help.
Restating the NAS Plex server did not help.
Reinstalled the Shield did not solve the problem.
Having the same problem at NVIDIA Shield for a long time. Please address this one as it is a really nasty bug (and while at it look into other long remaining bugs as well, maybe consider to port PlexAMP to Android TV/Shield in the process).