I have the same issue and the only way I find to kinda fix it is:
1 When you start ultimate team, go to moments, play any moments and when you finish and go back to the menu you will have the FPS dropped already
2 leave ultimate team and go to settings and graphics and reset to default, save and go back, as soon as you go back FPS should be normal again. Go again into graphics and set the graphics you are using, in my case I use medium.
3 you can go back into ultimate team and there should be no problem, there are rare cases when it happens again, you just need to repeat the process
I hope this works for you