Brake issues

[Rrawlings]

Set off this morning to work and all was good then started hitting slow traffic and the free play disappeared and then the brake started sticking again. Got moving at a decent speed again so bike cooled down and it was free as a bird at the next junction I pulled up at. So does it sound like still air in the system or should I get a master cylinder? I could have sworn that the bleeding was good and was free of air but I guess I could be wrong. The fluid level is halfway to allow for expansion just in case too