Since there is nothing you can do to prevent it, just try to plan around it. For example, don't plan on a big man with 20 WE to reach his Stamina cap because he will like gain 5 pts during the season and then lose 4 pts in the offseason, thereby negating what was gained. So just know going in that it can be a tricky rating to increase and if you really need it then you could be hurting. It can be really frustrating sometimes.