Welcome!
Have you tried to make a clear bead to see what is happening to your release? You may be overheating it and that will cause it to crack, as others have said. It's possible your glass is sticking to the mandrel. It's important to remember to treat your bead release gently because even the best won't stand up to heavy abuse, especially if you cook it from the get go.
Over time on a very intense bead, it may flake off above and below the bead. This is okay as long as your primary bead core does not shift. In fact your best bet is to lay down a thin barrel of glass, and take care of the ends right then. Ideally from that point forward, your ends and your bead release underneath the glass should never be molten or heated to bright orange. Great beads are often done in layers, even if it's just two.
Lastly, how are you dipping your mandrels? Pulling them out very slow actually leaves more release than pulling them out fast. If it's too thick of a coat, again it doesn't matter how good the release is, you'll have cracking issues.
Like I said, make a clear bead, just like you always do. See what's going on underneath. If you see mandrel, or glints of grey, or white flecks (the release) mixed in your glass.... There ya go.
