If there's no entry in the log files, then it might be a javascript error.
It probably won't be easy to get the javascript error out of the console on mobile.
If you are able to reproduce on our demo websites (beta or nightly), then we get javascript errors reported to us.
If you have third-party extensions installed, you could try disabling them one by one to see if the issue goes away. Then you might be able to pinpoint which one causes the issue.