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do i dare SUGGEST THIS :

from my old career with Planks.....what you describe reminds me of problems that were prevalent in the old days, (even not so old days)

on the ground, if the TRANSMITTER ir TOO CLOSE to the RECEIVER, it swamps, over-rides, glitches, etc etc

An experiment, for what it's worth, costs you nothing, : try not leaning over the helicopter with the TX in your hands. Rather step back 10 feet. I bet everything STABILIZES

valueless suggestion ? no sweat, NO CHARGE