Ive got a more up to date web-build of the tool hosted here that you can try out if you'd like. I will be getting an updated binary out asap as I continue to add some more features.
Theres also an updated binary on this itch page that may also have resolved some of your issues. Ive updated to the latest raylib which added some fixes for various model types and exports.
https://signalspike.games/spectre-pixelator/