It’s your front derailleur cage, if they get bent too many times then it loses its strength and just flex’s out when under hard shifts. It basically just bows out and now the cage is too pliable. Unfortunately you need a complete new Di2 front derailleur. Even if you bend it back it won’t work, the metal is now too soft.
It happened to me 3 years ago with my ultegra Di2 front derailleur and I was totally stumped for a week or 2 until I figured it out.