Master cylinder?? Issue.

If the master is a drum/ disk cylinder, it will have residual pressure valve on the drum connection, so if reversed, it might hold the disks in some
Determine where the pressure is releasing/ holding.

Might be a piston problem, or piston not returning. Some have claimed hose problems. Sometimes disks can wear tapered (non parallel) or worn caliper / bracket/ hardware can misalign the caliper