The holy list of potential browser issues it is then.
- Clear cache, close all browser windows, reopen, and try again
- Disable all browser extensions and try again
- Open an incognito window and try again
- Try a different browser with all extensions disabled and try again
- Try a different machine and a browser with all extensions disabled and try again
- Try a different machine on a different network and try again
I also wonder, if you can't duplicate the issue yourself, if the user is zoomed in on the page you're talking about which can cause interesting layout issues. Make sure the zoom is normal