Here's a new one on me:
In a sequence which so far has 1st strings, 2nd strings and Violas, there's one particular note for the Violas, B4, which won't play for the full length I need. I've looked at the Event Views, where all MIDI data is listed, for each of the tracks. There's nothing there that shouldn't be.
Experimenting, in Piano Roll View, I moved the B4 up a half step, and it played for the correct duration. It also was fine when I shifted down a half step.
This note stops after one beat even if the Violas track is soloed.
My work around--I changed the note to a C and used pitch bend for that one B4. Awkward--at least I can keep working.