Repeating my reply to your support email:
Did you try loading save from before that point?
Does this happen if you start a new game, make a manual save and then load?
Try browsing to the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition\LevelCache' folder and delete the contents. A corrupt file there can cause problems when saving or loading.
Try creating a new profile and exit the game, copy your latest save from the current profile to the new one, restart the game and see if that gets it working.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition\PlayerProfiles\<ProfileName>\Savegames\Story' folder.
If applicable, disable Steam cloud support either globally (in the client click on the Steam menu and select Settings, and then Cloud) or just for this game (in the library right click Divinity: Original Sin 2 and select Properties, then switch to the Updates tab and check the Steam Cloud section).
Alternately, exit out of the Steam client, or Galaxy for GOG, and just start the game directly from the '..\SteamApps\common\Divinity Original Sin 2\DefEd\bin\EoCApp.exe' executable when required.
Next, try browsing to the '..\Documents\Larian Studios' folder and rename the 'Divinity Original Sin 2 Definitive Edition' subfolder.
This folder contains the saved games, configuration files and a level cache folder. Deleting or renaming it will get the game to recreate it on startup; playing the game from a different Windows user account would effectively do the same thing. With Steam / Galaxy running and cloud support enabled, the client would just download the cloud copy of your existing profile.
After that, start D:OS 2 DE, create a new profile and see if you can start a new game and save/load. Exit and then copy a couple saves from the renamed folder into the newly created profile's ..\Savegames\Story folder. If that lets you load the saves properly, move the rest of the saves over.
If that doesn't work either, delete the new My Documents D:OS 2 folder and rename the original back again.
If a new game is fine but recent saves in your current playthrough have this problem even in a different profile, check the contents of the save folders. Each save folder should contain the save data in an lsv file and a screenshot png file. If there are multiple data files (ie an lsv.old file, or the uncompressed data files/folders) that could account for the problem. In that case, try separating the files into different folders.
In that case, please reply to the support email with your latest save (or a Dropbox or Google drive link, etc) as well as the most recent working save and oldest that loads to the same place. If you are using any non-Larian mods, also include a list of those enabled and/or the modsettings.lsx file from your profile folder.
In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder' (and similarly in OSX/Finder).