shifts side-bar

Are you sure it isn’t just shifting the page enough that the scrollbars appear? If that is the problem you can force scroll bars to appear always and that way things don’t shift.

https://stackoverflow.com/questions/1202425/making-the-main-scrollbar-always-visible

Thanks for your response, I tried it again to check what was happening with the scroll bars and it seems the problem has now resolved itself somehow.