I hear you. Same problem. I had a fast trainer who turned 22 and now he gains 38 when he trains high on a practice match. I am very pissed off, I invested a lot of green packs to get him an aerial defender SA, with the objective to keep him for several seasons as my main DC, and now he is stuck. I guess they want to promote that people buy and sell more and more players, almost forcing you to change the whole team every season.