Do you reproduce ?
1/ Create an audio mono track
2/ record a first event
3/ record a second event
4/ double click on the first event, in the track edit widons select “solo” and play => you hear the event in solo mode, OK
5/ create a container of both event
6/ double click on the container
7/ you see the both event in the container editor
8/ double click on one event of the container, you acces to the audio editor of the event
9/ select solo and play => nothing to hear !
It seems that the solo button in the audio editor does not work when editing an audio event within a container. The solo button in the audio editor works only if the event is not part of a container.