Raymarine ST2000+ Autopilot

We have a ST2000 Autopilot fitted to our Contessa.  We had a bracket made to fit the tiller by Sims Marine and that was done elegantly.  However because the tiller moves up and down vertically the tiller drops when underway and connected to the autopilot.  This either pulls the Autohelm out of its, brass male/female plug on the cockpit seat or it simply disconnects from the tiller.  Somebody must have cracked this issue as it renders to autopilot totally unreliable except for very short periods when watched. We’ve tried tightening the tiller to make it move vertically less, but this doesn’t crack the problem.  Ian S