I think I may have stumbled onto a (recent?) bug which occurs when combining tied tuplets.
In the attached screenshot, I selected the Violin 1 and 2 measures, copied them, then pasted into the empty Viola measure using the “Paste Special → Reduce” menu item. Despite the violins having the same exact rhythm, the resultant viola measure isn’t uniform. I am definitely selecting the entire violin measures (including the triplet "3"s), so I’m not sure what’s happening.
This also occurs when using “Paste Special → Move to Staff Above (/Below)” to combine the violins.
Interestingly, this is only a problem when tuplets have one or more tied notes.
Should be pretty easy to replicate this based on the above instructions, but let me know if more info is needed.
Thanks!