In my save I have 2 developmental companies, and they are all filled with people I hired. I've re-signed quite a few of them because I received notification about their contracts expiring soon thru the email. Soooo, I don't think that is actually your problem.
You might have the same problem I ran into when I first opened one of the companies. If someone turns in their notice that they are leaving your company, like when they are on a handshake deal, it doesn't notify you they are leaving your developmental company like it would if they were on your main roster. Got kinda annoying going to see what my developmental was putting on for shows and seeing in the news that "Ricky Banderas Quits UWL," even tho I signed him.
Honestly it's probably a glitch in the game tho. The game probably had Ricky Banderas turn in his resignation to the AI controlled developmental, as it's probably coded that way. Would be a nice fix tho.