I add a vst instrument. Add my notes in midi editing. Play. Sounds works. Vst instrument playing fine.

Select a different channel. Add a vst fx. Save.

Push play.

Original vst instrument stops playing sound but indicates it's playing with audio bars moving.

Re add same vst and attach to same channel.

Channel works again.

But if I add any other effect or vst to another channel, it breaks again.