Barkley on 03 November 2018
Have you tried contacting them directly about this issue? If they confirm it is an issue for matchmaking have you tried asking if they'll change your PSN accounts region to JPN?
If there actually is a matchmaking problem, it will be on a game-by-game basis, as some games will use there own matchmaking systems, rocket league/fortnite for example.
And yes DLC for games only works if purchased on an account with the same region as the game.
