That’s a weird one.  Are both the Sub and whatever your bonding it to both on the same firmware?  Should be 16.5 (build 82.2-59204).

Yes they are

Playbar: Living Room
Serial Number: 00-0E-58-BA-B2-FE:9
Sonos OS: S2
Version: 16.5 (build 82259204)
Hardware Version: 1.9.1.10-2.0
Series ID: A100
IP Address: 192.168.1.192
Audio In: Stereo PCM 2.0
WM: 1
OTP: 
---------------------------------
Sub Mini: Sub Mini
Serial Number: F0-F6-C1-03-5D-BE:3
Sonos OS: S2
Version: 16.5 (build 82259204)
Hardware Version: 1.37.1.7-2.1
Series ID: A100
IP Address: 192.168.1.191
WM: 2

​@Yorkyuser,

Just a suggestion…

Have you tried removing the local library from the unbonded PlayBar and then bonding the Sub to the PlayBar first and then adding the library-path/user-credentials afterwards? 

Nope, will try though.

Even though Sonos support say there is a problem with th emusic libarary on android. Always works on my windows laptop, but that is not a convenient way to control my music

Are you sure you’re not using an old HTTP library share as mentioned in the attached (put out by Sonos in their App last April)?

HTTP shares are no longer supported by the Sonos ‘mobile’ Apps - you need to use an SMBv2 (or higher) sharing protocol for the library to be accessible via the new App.

​@Yorkyuser,

I would suggest/recommend to add the local library back to the setup using the Sonos mobile App only, rather than the desktop App, although the third ‘NAS’ library option can be used too in the desktop App, but definitely don’t use the first two "add a library" options as they’re HTTP and no longer supported in the new mobile Sonos App.

Thanks for all your suggestions, but I have been through these with Sonos support before and got nowhere. 

Yes my music is on NAS smbv2.

After I add the library path, username and pasword, the app spends it’s time adding new content. When it’s finsihed, the library pathname is shown (so the app has recognised the path and added it), but I don’t see it on the main screen under ‘Your Sources’. Remove the Sub Mini and it appears !!