I don’t know if you have fixed your problem by this time, but anyway here it go. ??

Most companies have decided stop considering IE as it has a lot of compatibility problems.

You could try one of these theses that claim support to IE 11: https://www.ads-software.com/themes/search/ie11/

Have in mind that this could also be a problem on plugins that do not support IE 11, so please take a look into your plugins.

You could also recommend other browsers to your users as Edge (Microsoft as well), Mozilla Firefox or Google Chrome.