I don't belive that a player is lost suddenly, I think that like happened to me with Edgar Davids, the player need a level of stars in the attack skills and defense skills (probably defense) to recovery the % effectiveness in free kicks...
In the case of Edgar Davids he was a very special MC because was proggrammed to do the same action in the 70% of the matches and score, the action have a name in spanish that I can not translate and rarely Ive seeen in another player, but basically is a hard shoot from far away suddenly that becomes a goal.
When seasons passed and the attacking skills of this layer were lower than 5*, he lost this ability, but I trained him and again recovered the action he did.
Train mate, as I've said I don't belive that this game is proggrammed in a very complicated mode, that say that with 26 years the player loose an ability or a %.... the % or ability is lost with the Quality decreasing.