Minecraft ps4 bug psn account already linked

Hi,

My son bought Minecraft on his PS4 a few weeks ago. I'm not sure which version I indicated.
Last week the screen got stuck on "MOJANG". Impossible to play. We uninstall the game, and then we reinstalled the game.
since then my son can no longer play with his friends. it is displayed that his account is already assigned to another PSN account.
I tried with my PSN account but same bug ...
These friends have the same bug ...
do you have a solution please? Can you help us ?
apologies for my rough english