Hi
Does it do this on multiple iphone11 pro devices? Or just one in particular?
Are you perhaps able to route the traffic from the phone(s) with the problem through a machine running Wireshark or some other packet sniffer to see if a certain network request is taking a long time? This might also be done with port mirroring on a switch instead of routing traffic through the sniffer if you have a switch that supports port mirroring.