The audio is playing back my score, but somewhere along the way it started bypassing the mixer. That is, the mixer controls do nothing now. The screenshot shows the whole window. The mixer used to work until I started changing things. Bad idea, I guess.
I think I figured it out. Anyway, it works now. Apparently moving an HSSE instrument from one channel to another is a no-no without further action.
If you edit the instruments in the HALion player yourself, Dorico will not make any more automatic changes, because it doesn’t know how to avoid overwriting what you changed manually.
If you want to “delete all your manual edits and start again”, go to Play / Payback template and apply the template you want to use.