Rhidian, there is a solution to the issue.

Quote
Issues downloading the mod? Try this: (thanks to seraJard):
if you can't find this mod in your mod directory after downloaded, you should find your downloaded mod file in this location.

Dir~\Steam\userdata\

Search for: '4_player_mode*.pak' then you will get its location.
Move this file to the '~\Documents\Larian Studios\Divinity Original Sin\Mods'


Added on my mod subscription page.