ADC channels are malfunctional

The Moku Pro device we have now has the problem of malfunctional ADC channels.
The 4th ADC input has a strong fluctuation noise when not connected, make it almost unusable.
Any solution to solve this problem? I try to contact the support email address about this issue, but no one reply to me.

Hi Jian,

Sorry for the delay in response, I have followed up with you through email.

Kind regards,