If the problem appears to be specific to a particular project, we probably need to see the project itself, together with the steps we need to take to reproduce the issue.
There have in the past been some bugs that exhibit a little like this: you make an edit to an instrument, and when you play back, one or more instruments are unexpectedly missing. This happens because Dorico invalidates the playback data for the edited instruments, but doesn’t then recreate the playback data for all instruments. However, we’ve fixed all such problems that we have ever found, so there may be something else at play. We would need to see the project and understand what edits you’re making to find out.