912ULS large RPM drop on run up

I have a new Rotax 912ULS. I have a traditional keyed ignition switch with Off, Left, Right, Both and Start. I am experiencing a large rpm drop from 3,500 rpm to around 2,650 rpm on the left side with rough running when I do the run up checks. The right side only drops around 150 rpm. The engine seems to be running normally on Both but it's not as smooth as my old 912UL.

I checked out the Lockwood video checking first the choke on the 'bad side' and it didn't seem to make much of a difference so isn't related to carburation.

I switched the horizontally mounted six pin connectors to see if the problem moved to the other side. It did not, so I put them back the way they were.

Next I switched the vertically mounted six pin connectors to see if the problem moved to the other side. It did not, still on the left side.

I figured it wasn't anything on the engine so it pointed to the P-leads. I switched the P-lead pins from one connector block to the other and reduced RPM and rough running moved to the right side. So the issue seems to be related to the p-leads or ignition switch.

I checked continuity of the P-leads and they all checked out ok, opening or grounding determined by the switch position. I checked the resistance of the P-leads when in the grounded position and they all read 0.00 ohms on the meter. When open, the meter didn't show anything so obviously an open circuit as you would expect.

I plan to make up a new set of P-leads with a pair of toggle switches so that I can by-pass the ignition switch but I'm at a bit of a loss as to why P-leads or ignition switch might cause rough running when their only job is to either open or ground the ignition boxes.

Carbs are balanced and all the trigger gaps are correct. Anything else I should be looking at?