Lagging after saving

Hello--

I've recently been experiencing some extreme lag after saving a fresco file, leaving my computer for a few hours, and returning/reopening the file. The file will be completely lag-free for the entire time up until I save the file, and then once I return a day or two later, I have permanent substantial lag when drawing, zooming in/out, picking colors, and so on. I have fast internet and my files aren't all that complex; I only use pixel brushes, no vector brushes. Any idea how to fix this?

Thank you