45 to 50 seconds delay in getting Apple Captive Portal to appear

We have recently been encountering an issue with a 45 to 50 seconds waiting time in getting apple captive portal to appear for user authentication on our newer iPads/iPhone models in campus.

This issue is seen on newer models of iOS devices like iPhone X, iPhone 12, iPad Air 4 and iPad 10.2 running the latest iOS 14.2. I have an old iPad Air 1 running IOS 12.4 and captive portal works fine.

Our Firewall vendor support confirmed that the slowness is not due from the firewall and the captive portal request and response traffic was confirmed to be working smoothly. However, from a packet capture analysis session they setup to troubleshoot the issue, they saw an approximate of 45 seconds delay before new requests can be seen coming from the iOS device after you connect to the Wi-Fi SSID. This delay is what we are seeing on our iOS, hence we have to wait this period of time before getting the captive portal to appear to get authenticated.

has anyone been seeing the same thing on your captive portal environment? is there a solution to this coming from apple?