It happened to me a bunch of time, in arena, or as shown here, on gauntlet.
If FGE gets passive dissable before battle start, the game will freeze. I believe it happened every time he faced ghost of the navigator... but not exclusiveely.
See image:
https://ibb.co/GMhf6bL
Edit: also happens in cosmos or dungeons.
Was trying FGE to disable valor talismans in cosmic dungeon, and it freezes 1st round
