onResume() not immediately called on android (5-60 seconds delay)


I’m currently testing my app on Samsung Galaxy S4 (4.3) with about 300MB memory left on the device.
When I start my app, wait till sleep mode is activated, wait for another 2-5 minutes and then unlock the device, my app is freezing and onResume() is not called. I have to wait some time (5-60seconds) until I can continue using my app.

Does this behavior occur because javascript (and timers) are paused when app is in background? Because when I try to reproduce this bug with a very simple view (just login screen without much services and code in total), onResume() is almost called immediately.


EDIT: Or could ajax requests be the reasons for this bug?