Tranfer values are really confusing. My players values seem to crash before every transfer window leading to loads of pathetically small bids from big clubs that unsettle my players but I can't sell them as I'm getting offers of £5m for players that would cost me £70m+ to replace. I keep on getting it so I decided to keep track of a few of my players values over a few months. It has nothing to do with contract length or anything as all of these players have many years left on their contract and I guarantee their values will go up again after the transfer window.
It means I spend every transfer window just rejecting endless really low bids. Very frustrating.