Drawings disappearing, seemingly randomly?

Hi all,
Ever since I start using Harmony a few months ago, every once in a while I will have a random drawing get deleted (or sometimes get replaced by another drawing in my scene). If I notice it soon enough, I can usually “undo” it, but sometimes I don’t notice it until a while later. It shows up as “timeline: drop” on the list of actions that I can undo. I don’t see anything about “timeline: drop” anywhere and it doesn’t seem like there is a shortcut that I have set up for this action. It seems like maybe I am accidentally clicking on the frame in the timeline section with my pen and dragging it or something? But I can’t for the life of me figure out what keeps deleting drawings.
Has anyone had this happen before?