Brakes have locked up while driving and will stay that until the car is stopped

When it happens again, crack open the steel lines at the master cylinder to see if the brakes release. If they do, suspect the fluid is contaminated with petroleum product. That will cause all rubber parts to swell and the expanded lip seals will prevent the brake fluid from going through the return ports to the reservoir. You might also loosen the master cylinder mounting bolts two turns each and pull it forward. If that works, the push rod is adjusted too long, but that wouldn't happen on its own unless someone was in there or replaced the master cylinder with one that is a little different.

If any repairs was done at the pedal, check the pedal to booster push rod clearance. If there is insufficient clarance, the master cylinder piston would not return fully for fluids to return when pedal is released. That would result in the brakes seizing when the fluids heats up.

Is only specific wheel locking up or both front/rear in tandem?

This is becasue the caliper slides are frozen. Here is a guide to help you see what to do to fix the problem.

https://www.2carpros.com/articles/how-to-replace-front-brake-pads-and-rotors-fwd

Please let us know what happens and upload pictures or videos of the problem.

Cheers, Ken