[Vulcan Grey]

What color is the brake fluid after that track event? If the pads were riding on the rotor too much, as they would be if the hand brake was mis-adjusted, then the fluid will be black and full of bubbles.

Since you didn't mention a soft pedal, I'm going to assume that the problem is that you were going over the temperature limit for the pads and their friction was increasing with the increasing heat and the bad material was fusing to the rotor, causing the vibration and then a sticky feeling.

How do the pads look?

If your sliding surfaces for your pads were sticking, or the front pistons or rear caliper slides, then you should have also had a soft pedal from boiling the fluid.

I had something similar with my brakes, started off fine, then started to groan, then vibrate, and then the friction levels went through the roof, and the pads felt like they were fusing to the rotor. Once they cooled, everything was fine until they got hot again in the next session. Turned out the pad material was too soft and rated for a lower temperature than I was reaching.

A change of pad material, along with proper bedding in, or brake cooling ducts might solve it.

 

[Vulcan Grey]

Agree with Robains, check the easy obvious stuff first. Especially the rear parking brake mechanism.

Though in my case I have all 4 calipers with 4 pistons, full race Brembos with vented titanium pistons, and fully floating rotors, and no parking brake!

My calipers had also been recently rebuilt with new seals, the pedal stayed firm, and the pads are on loose simple slides that cannot bind, but it still felt like the car was getting difficult to move. Like the brakes were on, and the pads were glued to the rotors.