Ok it would appear you need epic games open in the background for this game to properly keep you in matchmaking. Don't really know why as I hadn't linked my acount but epic games seems to need to be open in the background and not updating. If you do that the multiplayer seems to work fine.

ive been having problems for months with the matchmaking. you interested in boosting some races between me and you. looking to complete the mp achievements i have left.