A quick FYI for the developers: this happened to me again, after introducing a new tom-tom staff to the score. The VST settings on my violin I and II staves got screwed up for whatever reason, so I changed them back to the proper VST, only once again to make the dreaded discovery that playback was dead.
Switching to a new voice and back again had no effect. The original voice remained permanently silent, even after I restarted Dorico.
I was able to fix the problem partially by switching to a different VST, then back to the proper one. Playback doesn’t respect playing techniques on the original voice, though. (So, muted strings play unmuted, for example.) Techniques are interpreted properly on the second voice, however. Really annoying.
This is Dorico 18.104.22.1686, by the way.