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That's something very abnormal though!
So you opened app and logged in and after quick surfing, closed app and that's all? Rest of the data is from background data and notifications? Hmmm

It seems like it. Maybe it was loading the news feed in background the second time I installed the app since I could not log in due to lag. It used 2.2GB on my WiFi.

It used the data in background, because I was far from home and had not touched the app.

I hope this info helps.

Yes it does, thanks! I have now implemented to disable API fetching when app is in background. Also working on Setting where user can choose to enable auto download of images or manual downloads to which user has to tap on image to see/download that image. ;)

Nice! Really like what you're doing!
Also one small thing annoyed me a bit: When images are still loading you're not able to scroll.
Thanks for being awesome!