If you can see the bug on your own device then you will probably have to use the 'trial and error' method and see if you can pinpoint the problem. e.g. Make some simple changes, upload the changes and re-test. If you don't have a copy of the device then it gets very awkward to test. You can download various emulators and try and find one that has the same problem and that will allow you to debug perhaps.
You say its a simple formatting problem but what exactly is the problem?
I often see cases of nav items that have dropped to a new line because the author just used padding and content size and expected it to fit all devices. If the issue is a text fitting issue then you have to allow plenty of breathing space and not just make things fit using padding and text content width.
Perhaps if you have a screenshot of the issue or a link to the site then some others here with similar devices may be able to look at it?
It is very awkward to debug the myriad of devices out there but some times simplifying the design can solve a lot of issues.