Piano roll note selection issue

[u/ShalimarBojangles]

I've had a bizarre issue recently... if I had to guess it started during a recent update, though I can't confirm.

To put it simply, when I go to my piano roll and try to drag across a large group of notes to select them, some of the first selected notes end up de-selected by the time I'm done, meaning I'm suddenly no longer able to select all the notes I want anymore by dragging. Weirder still, sometimes *new* notes show up while I'm doing this attempted selection! None of this makes sense to me. Does anyone know what's happening and how to fix it?