Brakes locking up
 

Had few issues, with air in my brakes, few weeks back. Got that issue taken care of. Rode it this weekend, and now thing is locking up, while driving it. There is plenty of slack in the assembly when start out. But then after while, brakes lockup on the disk. I try to loosen it up, but seems not to do any good.
After while, it cools down, brakes are back to normal. 3 times, take it back out, they would lock up after about 5 mins of riding. Cool down for little bit, brakes good, then would lock up a little later. I think the last time it was drove, it latest a lot longer before they locked up.
Any Idea what's going on?

Check the adjustment of the brake pedal to master. If too tight this will happen.

Could there be water in the brake fluid? If water gets in, it expands when it gets hot and presses on the brake piston. After it cools down, the pressure is relieved.