Group Key Exhange Timeout

Since upgrading to 6.1 I have been getting group key exchange timeout errors. I’ve now upgraded to 6.4 and the same issue is still there. The station is dropped about 10 times per day. I’ve searched the forums and there doesn’t seem to be a definitive fix.
I’ve tried hiding the SSID and changing frequency with no luck. Disabling WPA is not an option.
I’ve looked at this http://wiki.mikrotik.com/wiki/Wireless_Debug_Logs but it doesn’t have any advice or anything useful at all really.

My 711UA-2HnD is about 6 months old and I did not get them on my previous - could it be the router itself? Nothing at all has changed on the Ubiquiti end.

MikroTik - bridge

/interface wireless security-profiles
set [ find default=yes ] group-ciphers="" supplicant-identity=MikroTik \
    unicast-ciphers=""
add authentication-types=wpa2-psk eap-methods="" management-protection=\
    allowed mode=dynamic-keys name=wpa2 supplicant-identity="" \
    wpa2-pre-shared-key=XXXX
/interface wireless
set 0 antenna-gain=11 band=2ghz-b/g country=australia disabled=no \
    frequency-mode=regulatory-domain l2mtu=2290 mode=bridge name=wlan \
    security-profile=wpa2 wds-default-bridge=wds-bridge wds-mode=dynamic \
    wireless-protocol=802.11

and the log

oct/15 08:20:30 wireless,info debug: XXXX@wlan: disconnected, group k
ey exchange timeout

UBNT AirGrid - Station WDS

Oct 12 19:07:07 wireless: ath0     Received deauth from XXXX. Reason: Group key handshake timeout (16).
Oct 12 19:07:07 wireless: ath0     New Access Point/Cell address:Not-Associated
Oct 12 19:07:07 wpa-supplicant: CTRL-EVENT-DISCONNECTED - Disconnect event - remove keys

This use to be cause a bug in wireless client encryption. Common in hotspots. when you don’t have 100% control of clients. Try to change encryption settings. I don’t know about your setup. try to set wps2 psk - aes ccm

Thanks. I’m already using wpa2-psk.

but not group-ciphers=aes-ccm

In WinBox, this is ticked.