The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
Same happened to me, tried to move all my maps and mods from OneDrive to local folders, and then set the directory in FAF. Tells me "Oops. This Directory Isn't Empty"
So then I set the directory to empty folders, copy pasted maps and mods in there, but then the directory was reset to the original OneDrive directory
