I was getting the error code so it may be different but similar. Another thing I noticed is it only happened when I switched regions from NA to SA. NA was working but SA wouldn’t let me create a game with any seasonal characters.
It happened on another account and even just deleting an NS character also fixed it so it seems that if you update the hero list, that might be enough.
I’d suggest having him go on NA server and either create or delete a character then try and see if that fixes it for the EU hero list as well. Let me know if it works, good luck.