The double arrow inside the dashed box labeled "I Relay Disc" represents a small wiper on the I relay that gets rotated as the relay advances. The wiper connects different points on the contact board beneath it. The I relay has 10 positions so this pattern is repeated twice on the contact board that controls the lights. Chances are that the wiper that controls the arrow lights isn't making reliable contact with all of the positions on the contact board.
You may be able to manually advance the I relay and see the arrows on the playfield advance. That would help you identify which contacts aren't reliable.
Note that there are two wipers and two contact boards so check the wire colors to identify which board controls the lights.