[Steven Zahm]

@ Magnus

This is nearly always a fatal JavaScript error which is almost caused my another plugin or the theme. You can determine if this is the case by opening the page in Chrome, hit the F12 key and then click the Console tab. All page rendering errors should be listed and the cause of the error and file on the right hand side of the console. Sometimes the file name is enable to figure out which plugin is the source other times you have to mouse over the filename, the full path will then be shown. The full path nearly always can be used to figure which plugin is the source. This is the best advice I can give without a link to the pages having the issues.

If you can share a link to the pages with the errors I can take a look and possibly provide a solution.