Thank you for the details.
If the settings are same in your radio for both helicopters, then probably your first assumption is very probable.
The AIL pin could be loosing connection which is not good if it is used for SBUS2. But still we are not sure.
If changing the units is possible, it would be definitive proof.
If not, we can try to find other way together.

In any way if you can send the unit to us, we will fix the problem in a few minutes as we approximately know where the problem could be.
It looks like you are from Korea, I think that we could manage express shipping from you to allow returning the unit in a few days back to you.

That is great!
Does it mean that the problem is not happening anymore?

Yes, I can confirm that if the wifi module is too close to some servos, they can start to jitter. Similarly as when you have a telemetry receiver/module (depending on the power and modulation).
But usually it is enough to move or rotate the module.

This could theoretically also induce some noise on the telemetry line, but this is less likely.

I was busy with work and trips so I didn't have chance to fly much but since I changed my castle with new edge ESC It flied no problem.

If anything happen I want send it in winter season

Thank you for your support!