some times it shows the correct format and layout
If the site layout displays correctly sometimes and incorrectly on some occasions then the issue is more likely caused by your web host. It might not be delivering your files consistently. Kind of similar to the layout problem this guy had. The sidebars should only go below when viewing on a device with a width less than 800px. This is by design and you can turn it off on the
Frontier Options -> Misc
I personally have never experienced anything like this and I can’t see how this could be caused by the theme itself. The theme is simple enough that it should either just work or not at all. But like you said the issue only appears sometimes and not all the time.
You could also check your plugins, especially if you have caching plugins which might have been set up incorrectly.