Files keep getting completely broken when assigning VSTs in IRV

I keep running into an issue (since at least Dorico 3.5, now on where my file gets broken when using independent voice playback. Somehow, the program gets into a state where, when I click the “e” button to open up a VST (e.g. in the Track Inspector or VST list), it opens up a screen for a completely different VST, and does not playback correctly either.

For example, in the attached file, when I go to Play Mode, I can see that the 14th VST slot is assigned to Halion Sonic SE, but when I click the “e” icon to open it up, it opens an empty NotePerformer screen. It also does not play back through Halion Sonic SE at all.

test file 2.dorico (1009.4 KB)

Note: this test file is whittled down from a larger score, that’s why there are so many empty VST slots. I removed all the other staves and VSTs.

At this point, I haven’t found a workaround or fix. When a file gets into this state, adding a new VST and a new Player just results in more broken routing once I start assigning the new Player’s independent voices to the new VSTs.

UPDATE: I tried re-applying my playback template, which should reset everything that isn’t an IRV player, leaving me to go back and re-assign all of the IRV voices to the desired VST. But this strategy didn’t work - the file still opens the wrong VST and doesn’t playback correctly on multiple instruments.

Here’s a file that reliably reproduces the problem.
bugged file.dorico (1.3 MB)

Steps to reproduce:

  1. Open the file (note: NotePerformer 3 is my default Playback Template)
  2. Go to Play Mode
  3. In VST slot 14, add Halion Sonic SE
  4. Click the “e” icon in that slot once Halion has loaded
  5. Instead of Halion, an empty NotePerformer instance pops up

Interestingly, if I leave slot 14 blank and instead load Halion into slot 15 or higher, it seems to work just fine.