Naim Android App - 0 tracks added

I have 2 identical Kobo Arc7HD Android tablets running Android version 4.2.2 and the latest version of the Naim app.  I also have 2 UnitiQute Gen 1 streamers. The issue is that one of the tablets sees and  plays all the music on the Lacie NAS drive no problem on both Qutes. I can also play any music file using the remote handset. The other tablet sees all the files on the NAS but when I choose any song on either Qute it says "0 tracks were added". It was working fine then one day it started this behaviour. I have cleared the cache, rebooted the streamers & removed/reinstalled the app but to no avail. Any suggestions to remedy the issue? It is baffling to me why one of 2 identical tablets is misbehaving.  Thank you.