When mixing a previously ‘Live’ recording in Cubase there is a problem with Track Presets.
If I use the ‘Track Presets’ on any audio track the output goes and that track is silent…even if I remove all of the added effects etc the track stays silent…this can only be resolved by shutting down cubase and re-opening it. However, if I save it first then re-open the project that particular audio track will not play back…I have to start a new track and import the audio back in… This happens in version 9, 10, 11 and now 12. happens in both PC and Mac.
Check which plugins are involved. That would be the first I would try.
I had a long time issue with the UA TLA-100A and broken routing after copying it from one channel to another. Finally, there was a fix from UA that solved the problem I had.