Try logging out of the app and logging back in again. See if that helps.

Failing that, uninstall the app and reinstall it. 

Yes,  I tried logging in again.  In fact I had been logged out while I was away so what I described was for a fresh login anyway. 

So in addition to that I stopped the app and cleared the app data.  After starting the app again, and going through the "join existing system" wizard, it now displays the Sources list. However,  TV is missing;  only line-in is shown.  This is the opposite situation compared with what I reported last week,  where line-in was missing. 

I tried repeating the process and the TV returned to the list. So problem solved, but still no idea what is going on with the app.

Note - TV only appears as a source when you select the room that the soundbar is in. If another speaker/room is selected, TV won’t show. 

I don't know what you mean by this reply.  The home page has several items including Sources, each with a list.  That's what I'm describing. AFAICT the sources list in the Android app home pages is inconsistent.  Sometimes it is there, sometimes not.  Sometimes it shows all sources,  sometimes it omits one or more.  All for the same system setup with no apparent reason for the change except the phone leaving and then rejoining the network the Sonos Amp is connected to. The old app did not have this behaviour. 

What I mean is:

If you select the room your soundbar is in (eg Living Room) then on the home page you will see TV in your sources. 
If you select another speaker (eg Bedroom) then you will not see TV in your sources on the home page.

Yes.  The sources are always on their room details page. I have never noticed any problem with those pages.  But I'm describing how the home page Sources list is not always consistent, and in fact is mostly not consistent with those pages. One workaround is to clear the app data repeatedly until it picks up the correct information. Another is to make sure the TV is off for long enough for the Amp to release it,  and then rely on the line-in autoplay. Neither is ideal. 

Okay. But I’m talking about the home page sources list too if you read my post back.

I appreciate your further explanation.  However, I almost always have the room with the Amp,  TV and the CD player "selected". Everything I have described in the two topics I've posted has been with that room selected. 

To again emphasise the inconsistency of the "Your Sources" list,  this morning both TV and line-in are shown,  despite the fact that the CD player attached to line-in has been powered off for several days, during which only the TV was displayed as a source. 

And as another follow-up, after doing some household chores for a half-hour or so,  returning to the Android app, which was running in the background, I find that line-in has once again disappeared from the "My Sources" list. The only action I took in that time that might have been noticed by the Amp was to switch the TV off. The only thing I did that might have affected the app was to switch to a different Android application (email).

This is probably my final post on this topic. It is offered as another data point,  should anyone investigate the root cause. 

This morning,  on opening the (Andoid) app, My Sources displayed TV but not line-in. The line-in device (a dvd player) was powered off, just as it has been for several days.  The TV was on and operating.  I switched away from the app momentarily and then brought it to the foreground again.  Then both TV and line-in were in My Sources. 

Why is it so?

​@coder451 Does your setup have a Sonos bridge/gateway? - BR100

I find the only way to get my system to behave is to reboot this device. Services generally resume after this. 
Although I have noticed that this is becoming a requirement almost every time I want to use my system. Still on the original Sonos hardware. 
Cheers. 

If you still are using a Sonos BRIDGE, I would recommend retiring it. There are many cases of the power supply failing on it, which causes very difficult to track issues. Sonos, a long time ago, made each speaker have the capability of the BRIDGE, so you can’t take the Ethernet cable directly to a Sonos speaker, and have the same setup. Or, much more common these days, given the increased capability in routers, hang the Sonos directly from your WiFi.

If you have the need for a BRIDGE like device, I’d still recommend upgrading to the (now retired) BOOST, which is a much ‘newer’ and ‘better’ electronic device, which hasn’t shown the same propensity for power supply issues.