APM 2.6 and MP channel 6 tuning problem

I have used the Mission Planner channel 6 tuning in the past on this Tx and it worked fine but now it will not show any values other than the min and max that I set for PID.

When I do the radio calibration check, when I spin the pot the bar gradually raises and lowers as it should. When I try to tune with the channel and turn pot to say 25% and refresh I get min value. When I move the pot over 50% towards the high end and refresh I get max value. Before I would get values inbetween, now I only get min and max depending where the pot is on the scale.

Can anybody shed any light on this. I am current version on firmware and MP.

Thanks for your help

Hi, have you:

recalibrate your Tx
make sure channel 6 value covers the whole range
reassure with refresh button that the TUNE_HIGH and TUNE_LOW is what you are expecting