Happens to me often as well with Xbox one and wifi. It's weird because my internet connection for other games is never a problem, just FIFA. It's not all the time, but it happens enough to get on my nerves. Sometimes I'm able to fix it by unplugging my xbox for a minute and then powering back up, or resetting my internet router. It doesn't work every time, but maybe 60-70% of the time.
It's an awful feeling trying to play online, but knowing that my connection to the EA servers is like a ticking time bomb some days.