ever encounter this in SAI?
This usually happens after you save something that takes a while to save (large .sai files), don't freak out and don't think all hope is lost that you have to start over your artwork1. Just make a new layer on top of all the layers2. fill it in with any color or draw over a bunch of scribbles or lines wherever the corrupted areas are3. then hide that layer
in my case above, i had a multiply layer over the whole artwork when i saved this, so i just hide then unhide that layer to "shake off" the glitch
who knows, you might find this corruption effect one day