@coder451
Hello…
Regarding to the situation when CD was playing but you got no output I would check line in sensitivity on settings. Maybe it‘s set to low.
But that won’t affect the issue when line in is not shown in the app. I just know sometimes it takes a minute to see it there after the app starts. Btw on iOS that is no problem. But might also be an issue of network connection.
The behavior of Amp you described when using tv source imo is the expected one. In tv mode there is a follow up time where tv mode keeps the active source untill it‘s changed manually or by a new starting autoplay. So the last playing source before won‘t resume automatically.
This setup worked fine with the previous app version. Source level for the CD player is set to 2 (A/V), which seems ok as it is a DVD player. It seems to be always visible in the room properties (or whatever is the correct term). But it is not always in the main source list. This makes the manual control you mention problematic, in the sense that one never knows when it will be available.
@coder451
Just my personal experiences… even for av components I use level 4 to avoid autoplay issues. But that’s another topic.
In your case the missing input indeed might be an app issue. I suppose the app constantly looks for sources on the system and I don’t know if that is going via cloud services. But I suppose it is because of the new web app that needs that information. To check this you could open the web app on a different device via browser and take a look at it regarding to line in being available as a source.
@coder451 If you set the line in to autoplay via the app, when the app is available, subsequent successful use of the line in should just need a voltage sensed at the line in jacks of the relevant Sonos unit, with no role for the app to have the music to start as soon as the CD player starts playing a CD.
To summarise:
TV may take a while to relinquish its hold.
Amp senses voltage at the line-in terminals.
Possible app issue with not showing line-in in source list, removing it when it has previously been displayed, and taking a while to redisplay it when it has been turned off.
For me, the issue is that I can't switch from TV to CD on demand, I have to wait for the TV connection to time out. I think I can speed this up by power-cycling the Amp, which is not ideal.
Thanks for your suggestions.
Further to this…
To see how long the Amp would take to switch from TV to line- in, I turned the TV off, started the CD player and went out for a half- hour. As I left, the app had not listed line-in among the sources. Still no sound from the CD on return. But on opening the app I saw line-in listed. I'd been out of wi-fi range, so I'm guessing the Amp had detected the line-in voltage while I was out. However, I think it should have also started playing line-end through the speakers. This suggests the problem is not just with the app. It suggests the problem is also with the communication with the Amp, which not only doesn't play a source it knows about, but doesn't communicate the existence of that source to an already- connected app in a timely manner. Eventually, as I described, the information is transferred, but only after some other event such as reconnecting the app.
so I'm guessing the Amp had detected the line-in voltage while I was out. However, I think it should have also started playing line-end through the speakers.
If it has not started playing, your guess is wrong, but let Sonos Staff comment on this if they wish to or know enough to do so.
Assuming that you have set line in to autoplay on the Amp.
This new app has muddied the waters so much that giving what was straightforward troubleshooting advice also has become an issue.
A work-around for when there is no line-in in the main Sources list:
Start a service like a radio station that is displayed under Services or Recently Played, then start the line-in device. With autoplay on, the audio switches to the line-in device.
Investigating my work-around…
Start a local radio station, CD powered off. No line-in entry in main list, only TV.
Turn CD on, don't play CD yet. Radio keeps playing. No change to Sources list.
Start CD. After a few seconds, audio switches to CD.
Select radio station again, then tap play button. Radio audio plays. CD still not in Sources.
Leave it 15 minutes, CD still running, so voltage to line-in. Still no line-in in Sources.
Press CD stop button, wait a few seconds then press play. Radio keeps playing.
Power off CD player. Wait a minute. Power on CD, which starts playing automatically, and CD audio comes from the speakers. Still no line-in in Sources, even after restarting the app.
Stop app, clear data. Ensure CD and TV are powered on and running. Start app, join existing system. Line-in is displayed in Sources list.
Repeat previous, except with CD powered off. This time a welcome home drawer was displayed. I removed it before sweeping through all the pages. This time the Sources list contains only line-in, without TV. That was a surprise.
Repeat previous. This time swipe through all welcome screens. This time Sources contains TV and line-in.
I can at this point switch between CD and TV and back because line-in is in the list.
@coder451
To summarise again: 
Everything you have described yet except the „line in is not shown as source in app“ is normal expected behavior.
If you stop tv mode playback, NO source (streaming service and also line in) will resume playing automatically.
You have to start a new playback manually or by starting a new autoplay playback (a still playing autoplay source can’t be recognized as a new autoplay). Regarding to that and as you experienced yourself also line in has a short time of follow up time. If you look at the playback status, you will see that it’s still showing playback even you already stopped it. Instead of restarting your devices you also could have been waiting for about 30 seconds I estimate. Starting a new playback then would have been recognized as a new autostart playback.
The same is for tv mode… a currently still playing line in signal has to be restarted or imo much easier just switch to line in (if available ) manually.
The sometimes missing line in source in the app could depend on many reasons I think and might correlate with cloud service a I just said. But for me using iOS app it’s always there.
