Sniffing Android app's HTTPS traffic from Fiddler fails with only 'Tunnel To' entries in Fiddler

I am trying to capture HTTPS traffic from my rooted Android device (4.4.4) to analyze an undocumented protocol of an app. I've set up my Fiddler as a proxy and enabled HTTPS sniffing. I've installed the Fiddler's generated root certificate on my device. I've set up my proxy for my Wifi on my Android device.

• When I run my browser and navigate to any HTTP or HTTPS site, Fiddler can capture traffic successfully.

• When I run some apps (e.g. my own app which uses Parse as its backend), I can see all the HTTPS traffic to the servers, decrypted. So far so good.

• When I try to run that particular app, I can't get Fiddler to capture its traffic. Here's all I get on Fiddler:

URLs are some IP addresses:SSL (:443).

I've also tried using ProxyDroid. Interestingly, I was able to capture the traffic once, saw a decrypted HTTPS connection to that app's servers, but after that, it never captured again. I know that the app uses HTTPS, and not an unknown/other protocol.

How can I capture HTTPS traffic successfully, and why would Fiddler once work for that app, and suddenly stop working?

It appears to be specific to that app. I was successfully able to sniff all the other apps. That particular app probably uses SSL pinning: it checks for certificate within itself and doesn't allow fake certificates even if it's trusted by the device.