I’m guessing this is a bug that can be fixed in a future version. However, I can’t for the life of me figure out how to work around the issue (even with ugly notation) as I can’t get the top voice to allow triplets and the bottom to not.
Two possibilities in that dialogue seem possible, both help, neither are perfect:
Update snares (and all others that might be in triplet fills) to be in Voice 1, not Voice 2
Update snares (and all others …) to be in a new Voice 3
The first would avoid the specific problem in this thread, but would similarly struggle if ever the snares had a different tuplet than the cymbols.
The second helps - now the snares are more easily made independent, but isn’t ideal because simpler drum beats now are much more complicated to notate (see how the snare and the kicks are now separate voices):