It should already be fixed. Please email supportdos2@larian.com with the save that crashes when trying to overwrite it (or a Dropbox or Google drive link, etc).
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2\PlayerProfiles\<ProfileName>\Savegames\Story' folder.
In Windows Explorer you can zip file(s) and folder(s) by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder'.
If this is the same issue, it is possible to check the save folders, and see if there are extra files in them, and separate/delete as required. The saves should just be a png screenshot file and lsv save file, having the same name as the save folders; any other files (globals.lsf or a levelcache folder conataining lsf files) are intended to be temporary, and should have been removed once the compressed lsv file was created.
