[RESOLVED] Cannot play single player game, "Requires purchase of the base game"

I downloaded this from Epic Games Store on Sunday (free game) and have been playing since. I also played earlier this morning, no problem. When I try to play now, I keep getting the message "Requires purchase of the base game".

I don't know if this is Epic's fault, I've restarted my machine and also checked the EGS support scope and they state to log a request with the developer of the game itself.

Any ideas?