It's alright, that one's on me—I forgot to mention I recently updated to the latest SAI 2 build (2026.07.04), which no longer supports exporting to the legacy .sai format. It does seem the update changed a few things here and there, nothing to do with your work.. Since regsvr32 completes successfully and returns DllRegisterServer succeeded, the issue likely isn't with the DLL itself or its registration, but rather with how the new file format is being written or interpreted by the thumbnail handler
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!
So the file type has actually stayed largely the same and shouldn't be effected by the new version. I've tested both Alpha.2026.09.02 and the 2026.07.04 build. I did fix this bug and updated the latest build to address that but it probably doesn't address the bug you're describing in particular. Are you still seeing this issue on the new version? Have you tried any other attempts to resolve it?