Can you confirm that you have followed the steps required to enable capturing traffic from an iOS device? See the related documentation here. Alternatively, check if you are facing this issue related to different versions of TLS. In the very same thread, you will also find that some applications are using an extra layer of security through certificate pinning (see details here).
If your issue still persist, you could send us the exact steps you are taking so that we could reproduce the issue.
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