It seems to be only for a Fighter. First I tried creating a PhB standard human fighter with a custom background and it got stuck. Tried recreating it about 6x with brand new character sheets and in multiple games. I even tried to go all standard PhB options so I can delete and add custom things after, and nothing works. I did create a full custom Druid earlier today in the same game and it worked, as well as a random Artificer after. This issue seems to be specifically affecting Fighters. Also, I do not have the character sheet popped out.