In order to be sure that Fiddler is not hiding the session you can go to Help -> Troubleshoot. This will enable "Filter troubleshooting", which will show all sessions and those which would be normally hidden will be shown with strike-through font.
On the other hand, some apps use the so called "Certificate pinning". However, when we've seen such apps they refuse to work with Fiddler and does not load at all. In your case it works, so it seems that this is not the problem.
Another thought - when you inspect the tunnel session there will be presented information about the HTTPS handshake. You can check it, maybe the answer could be there.
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