The real problem to me is that the RX does not "stay bound". That requires further investigation, effort, and resolution before anything else occurs.

The flap problem sounds like you are using a separate channel for each side. Have you tried using a "Y" cable and only one channel?
If you try the "Y" cable, and the flaps behave like ailerons - - - You can go back to two channels, and reverse one in the TX. Or, it may be possible to move the servo to flap linkage and servo arm to the other side. Some of the RTF and "receiver ready" models used a reverse version of a servo in one or possibly two locations. The DX 6i has a monitor function that shows the servo movement/direction for each channel.

According to the model's instructions - - -
The servos should form a mirror-image pair, i.e. one left,one right. (This is the likely cause of aileron like behavior.)