Troubleshoot with Safari
In Safari you can enable Developer tools, as you see in this video:
JavaScript error debugging
Turn on Developer tools -> Click on Console and refresh the page. If there is a JavaScript or file loading error, this will write out the problem.
Page speed
Turn on Developer tools -> Click on Network and refresh the page. This will write out what is loading for how long on your website. This documentation can help you identify problems related to slow pages.