Hall sensor intermittent short
The adjacent wire that was tightly-bound to the wire shown in the previous photo was shorting intermittently. This essentially disabled the Hall sensor causing the motor to run slightly roughly and be unable to start from a stop when the rotor was in certain positions. This was one of my custom Hall harnesses I made for a 300-watt BMC motor. I was rather relieved to find that it was my error and that I did not receive a batch of defective Hall sensors! But, redoing the work was tedious.