I seem to have noticed that the player's attributes have stopped increasing. I'm referring to players under 23 as well. I keep training on balanced medium and attacking movement for the other option.
I solved it by clearing the game cache, but another question. if i varied the intensity on a monthly basis between medium to high would that make a difference on the players.
I think the higher the intensity is, the more they get out of the training in a positive way. If you are manager for a top team you should have it on high, but keep the players morale good.