Can't see folders on 1 of my 2 Synology NASs

I'm running 2 synology NASs, both running DSM-5565 update 2.

From my iPad running 4.5 of the Naim app I can see both NAS devices under the UPandP servers from both my mu-so and NDX.

I can see all of the folders on the 2nd NAS from both the mu-so and the NDX

I can see no folders on the 1st NAS from neither the mu-so nor the NDX.

Connecting to UPandP directly from the NDX I can see all folders and files.

I've followed the advice in Phil's sticky, but still no joy.

I've stopped and restarted the Music Server on the NASs and rebooted all devices, still no joy.

Any ideas out there ?