Lane B Rough Running + Lost 1000 rpm

Fellow Rotax experts,

I am dealing with a Lane B rough running with 1000 rpm lost symptom on a 2013 CTLSi. The aircraft has been using Rotax spark plugs but only recently changed the caps from NGK to Rotax. Customer stated that during cruise the Lane B warning light came on and showed a "Ignition coil 4 fault" message (This was on both lanes and engine run smooth). The roughness happens when it's switched to Lane B.

I downloaded the log & fault data, sent them to Rotax service center. They confirmed that it is an ignition problem and suggest to check the coil, cables, as well as the X2 connector where Lane B is getting the power from.

Since the problem is on Lane B, I went ahead and ruled out the possibilities downstream. Unfortunately, the problem persist.

Below is what have been done:

- Checked the resistance at primary & secondary side on Coil 2 & 4, all within the value

- Replaced Coil 2 & 4 with new

- Resistance checked on all spark plug caps, all good

- Replaced top 4 caps with new

- Continuity checked the ignition cables between coil 2 & 4 and Top 4 spark plugs, all normal

- Replaced ignition cables between coil 2 & 4 and top 4 spark plugs

- Replaced all 8 spark plugs (It's time to replace anyway)

- Checked for tight connection at X2 and made sure the O-ring is present

- Checked all 3 connections on the ECU

- Traced the entire wiring harness for obvious defect, didn't find anything

Is it worth the time to troubleshoot on Lane A side of coils & cables even it's not giving issue?

Can someone please help out?

Thanks a lot!