Why no sound?

I separated layers from the top track, below. From the beginning I hear the bass, but then in the selected loop area, if I solo the drums, I hear nothing. Clearly drums have waveform, and volume is up all the way.

If I solo other, then I hear most of the sounds.

Have you “Made extension permanent” for all of the actual Parts?

No. I was trying to map the song to measures and thought that if I heard the bass better, I would have the downbeats more accurately. but after the 12 bar bass intro, it disappears from the bass layer. I had wanted to tone down the horns to better hear the drums and since the separation wasn’t very good, I thought I would probably want to refine separations at some time. I hadn’t finished the mapping. While meanwhile I just wanted to hear the drums better and now they have no sound. How do I make an extension permanent? I don’t remember tracks dropping out in other projects where I separated. Oh I see where. did it and still no sound though. … Because the drum waveform has disappeared!

I’ve found that some operations in ARA result in no sound from an event, and that translates to no waveform if you “Make extension permanent” in that state.
Since you have dragged the layer out of SL, effectively creating a new audio clip, and it will have the extension active even though there is nothing being done on the clip at first, I believe the best course of action is to use Remove Extension (or selecting “No Extension” in the status line drop down menu). Usually this will fix it. But remember, if you have made any changes in ARA to that new event after draggint it onto the timeline they will be lost.

This is crazy. Yesterday I removed the extension and while the other tracks remained, I delted the empty drum track and did spectralyers on the original, only extracting the drum layer. When I put this layer back in and played with the rest, it was much louder, and I could hear what was going on.
Apparently, I didn’t save, as today, the drum track was empty again. I did the same operation, removing the drum track, and extensions, extracted the drum layer, which clearly has a waveform and made into a track, and now nothing at sounds, with all including the original, soloed. I did get a message that a serious problem occurred and I had to close cubase. Since I hadn’t done anything important, I didn’t save before closing. I was playing slong yesterday and now no sound and also the save from 4/3 a day before also has no sound.
Reverted to saved and no sound.

So by trying some other projects, I find that tracks with midi sound in the external mixer, but not any audio tracks. then I open cubase 13, and audio tracks play. In the studio, the assignments are the same and correct. too tired to go on, maybe rebooting will bring back capability. Try again tomorrow.