I got the same issue for a few players now.
At least for a player whom I would actually buy, I could cancel the transfer.
But there are 2 players whom I would sign by expiring contracts and I have no option to cancel them.
I hope if you can fix it some time it will work with old saves as well.
Let me know if you need me to upload my save file. I'm on the 24.1 version from the nov6 update, but the save was started with the beta version.
update: I managed to cancel those transfers through the transfer center, but there is no option to do it on the player's profile (or right clicking on their names)