iOS 15.2 Beta 4 fixed our issue. The feature is further tracked in the aformentioned webkit bug report

Just for reference, I created a WebKit Bug Report: https://bugs.webkit.org/show_bug.cgi?id=233752

Did you find any solution or cause for this issue?

I would also be thankful for an official statement regarding this issue. We have spend days with this issue without any notable improvements. It looks like the iPhone is is some kind of loop and is not processing the DTLS "Client Hello" messages. In Wireshark we always see just "DTLS" instead of "DTLSv1.2" when the issue occurs. We have two customers reporting this issue, one can't establish a connection at all, the other one has the issue every now and then. Our first thought is that "DTLSv1.0" is used, as it is not supported anymore by Safari we tried to pin it to "DTLSv1.2" but no luck. It appears Wireshark will display just "DTLS" as long as no "DTLS HelloVerifyRequest" is sent by the other side in the DTLS-Handshake process. Did someone have similar findings?

I am running iOS 15.2 Beta. We have an Cordova based application using WKWebView. We noticed that we are not able to communicate (Exchanging a Video feed) with the WebRTC client in some Networks. We suspect that there is some kind of DTLS issue as we can see an ICMP code 13 (Communication administratively filtered) response for a STUN binding request in Wireshark. Also in the iOS OS Log we can see that a UDP connection can not be established, which would explain the ICMP. The experimental feature did not fix the issue, also playing the the other flags you mentioned did nothing to improve the situation.