It's likely that my Sai2 code was not considering an edge-case in the file format that the latest version of Sai2 utilizes that I'll have to reverse-engineer. I notice some people on the GitHub page are running into similar issues, though with larger documents. Do your issues seem similar?
https://github.com/Wunkolo/SaiThumbs/issues/12
Either way, this may take a bit of time to reverse engineer!