Subject, but I'm getting a feeling that this is another Hyper Light Drifter situation where there's some per-installation encryption because when I transferred from Steam to GOG and now post Windows reinstall, both times preserving my save files, my progress is reset (and now presumably lost). I'm not sure that I particularly feel like replaying 2/3 of the game again.

Hi Tally! Sorry that this happened; Indivisible's Steam save files aren't cross-compatible between different Steam accounts or between Steam and non-Steam versions of the game, but our GOG save files aren't tied to a specific PC/install/account in any way.

If you still have the SAVEDATA.BIN file from GOG that wasn't working post Windows reinstall, I can take a look at it to see why it isn't loading. The best ways to reach me are to send it to me on Discord (username: Mr Peck#1980) or to email it to bugreports@labzerogames.com as an attachment.