[CA] [CA11] Rudder indicator reading incorrectly

[NomadAU]

Earlier this year I fitted an ACU 300 to my yacht, calibrated it successfully and had it working well for the short trip across the bay back to my mooring. That was back in February this year. A couple of months ago, thanks to a Raymarine forum append I read, I found I could use one of my i70s units to display the rudder position. Apart from configuring the screen, this also included having to configure a small offset (2 degrees) via my Axiom autopilot setup screen so that the display indicator was correct relative to the actual rudder position. So far so good.
Since then, I have updated the software for all the Raymarine components on the boat, using the Axiom MFD software update function which lists all the updates that can be applied. I also updated my Navionics charts (both chart and sonar). Apart from that, no other changes have been made and the autopilot has not been used since the initial trip back to my mooring earlier in the year.

So here's the problem. Yesterday I switched on the instruments to check they were still working and found that the rudder indicator on my i70s was reading completely wrong. With the rudder centered, the display was showing 42 degrees Starboard. I then tried using the Dockside Assistant to configure the autopilot, went through the normal centre, wheel to port, wheel to starboard, centre sequence but then got the error message 'inconsistent values'. I've since tried this several more times and get the same error. I've also checked the sensor but this is positioned correctly and hasn't been interfered with. I removed the sensor linkage and manually positioned the sensor arm to get some readings.
With the sensor arm secured in a fore and aft line it is reading 42 degrees Starboard
With the sensor arm released so its internal spring pushes it as far as it will go in my installation, it reads 4 degrees Port.
Clearly something has gone wrong with either the data being emitted by the sensor, or the interpretation of the data by the ACU 300. Seems to me more than coincidence that this appears to have occurred only after the software updates, but maybe that's just the paranoia of an experienced IT person!
Would appreciate advice on how to address this.

Cheers,
Mike