Had the same problem on a Seiko today,going like a train until you placed it face up, then it stopped, Checked the balance pinions they were OK, pallet pinions all OK, pulled the train bridge off again and gave all the pinions a microscopic examination, culprit was the third wheel lower pinion, not broken just damaged, even under the microscope it was hard to see, used another third wheel from the spares bin and problem solved.
So check all the pinions carefully, I had already checked these and thought they were OK!
Max