Wi-Fi Connection Error and MAC Address Limitation Issue on Fortigate60E (v7.4.5)

[Susumu_Kobashi]

Fortigate60E (v7.4.5)
There are 9 FortiAPs (v6.4.0 v7.4.4 mixed) hanging.

Currently, the SSID settings are set as follows and restricted by Mac address.

config wireless-controller vap
edit "AAAA"
set ssid "XXXXX"
set intra-vap-privacy enable
set schedule "always"
set address-group "WiFi_Allow_Mac"
set address-group-policy allow
next
end

WiFi_Allow_Mac There are many Mac addresses registered in the address group.
Recently, there have been more than 256 cases, but there has been an event that causes an error in the Wi-Fi connection.

Action: client-denial
Message: Client cc:d9:ac:xx:xx:xx denied (denied 4 times in one second).
STA denied on WTP due to VAP ACL

If you remove a few devices from the address group and reduce the number of devices, the connection will be successful.
Are there any restrictions that are not mentioned in the specification?