I tried the reset thinking the same as you but no joy, passed the customer to Stannah now because they were desperate to get his mother out of hospital.
Shame, it goes against the grain doing that but needs must and I did warn him he would be a quite a bit poorer after their visit
Just for future reference This sounds like a sofia seat swivel the fault you are describing almost certainly points to the power swivel pcb being faulty. The other stannah dual swivel model (starla or sienna) only has 1 swivel motor the sofia has 2 motors