Meru Wireless coverage fluctuating

Dears,

We have Meru wireless controller model mc3200 and the access points of model AP832i.

recently we encounter an issue in the coverage, it is fluctuating, i mean it is keep going up and down.

even if you test near the access point itself, the coverage is keep fluctuating up and down.

i have upgraded the controller and the APs to the latest version but still the same case.

any idea and advise about this case.

your fast response is highly appreciated.

Thank you