All my AP's now not stable up and down !!

[netmanb2k]

I have FortiGate 81E, i have 3 switches, and 10 AP's (5 221E and 3 224E outdoor)

Everything was working fine for long time

Today mid night all my AP's are not stable now going up and down every 10-15 min 

All ruing latest release 6.4 and the FortiGate 6.4.4.

The switches are stable with no issues only the AP's 

And AP's are connected to different switches 

Any ideas ?

[jhussain_FTNT]

Kindly provide the output of the below logs on the Fortigate

diag wireless-controller wlac -c wtp

Also you can increase the keep alive time by the below command.

#config wireless-controller global
#set max-retransmit 15
#end

# config wireless-controller timers
(timers) # set echo-interval 60
(timers) # end