The issue is that Windows users disconnected from WIFI network every 2~10 minutes, Mac users are less frequent but still get kicked off 1 or 2 times a day. We don't have such issue with any wired computers.
The coverage is good enough even for corners, and average number of users on each WiFi access point is around 10~30.
The DHCP least time is 21600s(5 hours)
By "kicked off" I mean the L2 connection failed. We use several different brand of WIFI APs in the network, 4 Unifi from Ubiquiti Networks, 1 Cisco, 1 Netgear, all have same issue...