sticky caliper

If that does not work then check brake tubing or even hoses for a kink or collapse. Even brand new hoses are crimped too much and slow or stop fluid.

Have an assistant apply pedal pressure and let off and check the drag. If you open the bleeder and the drag goes away then it’s hydraulic - if not then swap pads side to side before sanding anything. It could be crap in caliper or mechanical line up or something simple. Or just a thicker pad as stated above.
Good luck! Keep us posted. Fingers crossed you find it quickly.