Rudder channel sometimes moves with elevator stick

I've had a Devo 8s for 5 years now and recently I observed a problem where the rudder channel will sometimes move with elevator stick input. With this problem, I didn't want to take the risk of using the radio with any of my larger helicopters anymore so I decided to buy a used Devo 12s. But even the Devo 12s I received has the exact same issue of rudder drift with elevator stick input!! How can that be? Is this a common issue? I've tried searching if anyone else has reported such an issue but haven't found anything.

I tried unplugging the rudder pot from the circuit board and the issue still persists so it is not an issue with the rudder pot. The issue is seen with the stock walkera firmware and also the deviationtx firmware.

Here is a video of the problem. Observe the rudder channel (4th bar from left in the top row) move when elevator stick is moved.

Thanks I will try that. But isn't it odd that the exact same issue is seen on two units? One is a Devo 8s and the other is a Devo 12s. So I'm very doubtful that it is just dust causing the issue. I'm surprised how there are no other reports of such an issue.

I use Mode 2. Throttle and Rudder on the left stick. Elevator and Aileron on the right stick.

That is strange.
FWIW - I checked my 6S, 7E & 10 and none of them do that.

I examined the board and traced the traces but didn't find anything odd. This if of course just eyeballing. I've not done any continuity testing or coupling tests since they are beyond my scope. I used an air canister to blow over the board to get rid of any dust but it hasn't helped.

I tried a workaround and I think it should work for me. I connected the rudder pot to the aux2 input on the board. So now my rudder stick controls aux2. On any helicopter/plane I setup, I will connect the aux2 output on the receiver to the gyro (or rudder servo). Let me know if anyone sees a hazard of doing this.

One strange thing I observed. If I create a model and on channel 4 (rudder) I assign the "src" as aux2, then on the model screen, channel 4 has no drift, but on the "input monitor" screen the rudder channel has the drift. This was not the case earlier before I connected the rudder pot to aux2 (rudder pot was connected to rudder input on the board). Earlier both screens showed channel 4/rudder output drifting. If someone can shed light on this please do. For now I will not trust the rudder/channel 4 output and just use aux2 instead.

Edit: After thinking about this I think I get it. It's the input that is drifting. So when the input was rudder the drift will be seen on channel 4 in the model screen. Now that I changed the input to be aux2, the drift will not be seen on the model screen channel 4.