https://www.polygon.com/fortnite/2018/9/26/17906258/ps4-fortnite-account-nintendo-switch-unlocked

Sony has announced that cross-platform play is coming to PlayStation 4, starting with Fortnite. But cross-platform play wasn’t the real reason people were upset about how Sony was handling Fortnite accounts. The anger came from the launch of Fortnite on the Nintendo Switch during E3 this year, when players found out that any account that had been played on the PlayStation 4 couldn’t be used on the Nintendo Switch.

Not being able to play with your friends on other consoles was one thing, but being blocked from playing with your account at all on Nintendo Switch or Xbox One because you used it on PS4 is another. It felt like we should have been warned never to play Fortnite on PlayStation 4 if we wanted to play on Switch at a later date.