Unfortunately, I'm not sure what else to suggest, and the other person who reported this did not email back with an update if they were able to fix this (they were also quite thorough with their initial troubleshooting).
Saves are compatible between OSX, Windows and Linux, so even without cloud saves enabled, you would be able to manually copy the save folder over.
Each save is a folder in the '~/Documents/Larian Studios/Divinity Original Sin Enhanced Edition/PlayerProfiles/<ProfileName>/Savegames_patch' folder.
