As already said, it's usually wages too far away from what they should be although it can also be that the player has moved between clubs fairly recently and doesn't want to move again.

Should be noted that it's the manager that chooses the contract length. If you know a player is getting a boost but you don't want to keep him then ensure his contract runs out at the end of the season.

Otherwise you can just TRAN2 of course

Well without knowing the player number it sounds like he had a decent boost end of season and now his wages are out of touch with the value.

If he goes to another club those wages carry over to a new contract. If this rule didn't exist then he could be transferred between clubs for ever and always stay on the same wages. This is why this restriction exists which I am sure you can see now looking at the bigger picture. If there is a loophole I can promise you it's been spotted long long ago and blocked to keep the game fair for everyone.

You could have set his contract to expire on Week 33, given him a new one on Week 2 and then sold him to another club as the wages would be within the parameters