I can’t confirm that it happens in solo mode but I can confirm it does happen. It’s random…sometimes the track won’t make a sound if I start playback from KeyEditor when editing another track (which isn’t set to Solo mode or someting like that). Something fishy is going on here.
I also noticed a similar behaviour for duplicated instrument track and I’m 100% sure I did use duplicate on that problematic sampler track. So the culprit might even be in duplicating the track?