MAG check side A lower RPM than side B

The MAG check on my 2021 912ULS isn't working as usual.  I watched the video on what to check and here are my results if anyone could help me get to the next step;

 

2021 912ULS in an Aeroprakt A22LS

 

After warmup, I set the rpm to 4010.  MAG A off and rpms drop to 3770.  MAG B off and rpms drop to 3880 (what I would expect).   I pulled the plugs, which were new Rotax plugs installed about 5 months ago.  They looked okay but I cleaned them up and retested.  MAG A was then slightly better at ~3780.

 

Per the video on Rotax Owner I set the choke on MAG A; The RPM increased as expected but no change in how it ran, indicated a problem on the ignition side.  I swapped the vertical connectors and tested again; this time the lower RPM was on MAG B and again, the choke had no effect other than increasing the RPM.

 

I'm not sure where to go from here if anyone could advise.  One thing I've started to do is pull the spark plug caps and test them with an ohm meter.  The top plugs all test good.....haven't tested the bottom plugs yet.