I hope you are doing good.
I have created the below setup on your controller to check the connection failure issue on lab APs. Thereafter, I have mapped the wrong vlan under the Wlan settings to fail the clients to get an IP from the DHCP. So, the APs should show the connection failure rate in the UI.
1) Zone: Ruckus Test 3.6.2 and Wlan: 00Test-3.6.2 Client's devices were failed to connect to the SSID(00Test-3.6.2) due to the DHCP issue. I could see 100% connection failure rate and historical report of client's connection under the health Tab of the AP. The AP was displayed the accurate results in the UI.
2) Zone: Ruckus Test 3.5.1 and Wlan: 00Test-3.5.1 I have connected the same devices to the SSID(00Test-3.5.1) to check the failure rate and noticed that there were no connection failures reported on the AP for the clients who were failed to connect to the SSID.
I have analyzed the flagged APs(Default Zone) in your controller and could see the connection failures reported due to the DHCP failure. Client might have faced the difficulty to get an IP from the DHCP server at that moment. Please see the attached screenshot of historical report for your reference. The above test concludes that the connection failure algorithm is not working properly in the 3.5.1 software version and there is no miscalculation of connection failures in the 18.104.22.168.222 version.
As I informed earlier, the connection failure rate that is shown in the UI is a cumulative value of the AP. The AP would take into account Auth, Assoc, EAP, RADIUS and DHCP for reporting connection failures.Connection failures are calculated at 90 seconds interval. If during that time there are only failed attempts (even a single one) and no successful ones, the system will display 100% connection failure.