Animate 2021 constantly getting stuck on "Animate is processing strokes, please wait."

When using the classic brush tool, Animate will often freeze after a stroke, displaying a pop-up with a progress bar saying, "Animate is processing strokes, please wait." The progress bar never advances past zero, and I have to force quit and re-open the program. Fortunately due to autosave features I don't lose that much progress, but it's still very annoying. Any idea what could possibly be causing this issue and how to solve it?