I'm facing a weird situation. Office LAN configuration is :

* A Netgear router as the main router
* An Ubuntu PC with UniFi controller software
* 10 UniFi APs

At anytime, the latency between a computer and the main router using a wired connection is 0.300 ms and 0.400 ms. Using Wi-Fi, the latency can vary from 1 ms to 1000 ms and, eventually, a timeout. If at the exact same time, I check the latency using a wired computer, it's still 0.300ms. 

I checked the bandwidth and it's always low. I'm assuming a device on the network is creating latency. I installed ntop to monitor the network, but I found nothing obvious. 

Do you have any suggestions?