Ray, interesting charts, #177.
Concentrating on the 'certainly split' region, then this is coincident with change of stab trim.
As you note, which part of the system is driving the trim; which direction - presumably nose down.
Pilot trim switch input, but it is not clear if the AP was disengaged.
Or the AP, auto trim, unlikely re the stick deflection; but if so the direction should be consistent with the selected mode, which was …
Or AP overridden by stick deflection; is this CWS mode, and if so what would the trim be expected to do. Perhaps minimise the stick force as a 'follow up' trim function; but then why does the trim not stop / reverse when the sticks are reversed. The stick 'reversal' is coincident with the split region, where trim reversal might be expected, but with a split, which stick has priority.
Much of the above depends on the stick force felt by the pilot, which is affected by the elevator and trim positions and their relative position in feeding back the feel force.
We don't know what the pilots felt nor how that might have influenced their perception.