It looks like the gallery is probably working OK but the problem is that it is not visible on your web page (perhaps due to custom CSS or HTML errors on your web page).
I have checked your web page with the W3C Markup Validation Service and there are several HTML errors.
For example, your web page has 3 separate containers with id="menu-hoofdmenu". All ids on a web page should be unique. IE11 may not know which of these containers to apply #menu-hoofdmenu CSS rules to. You might expect it to apply #menu-hoofdmenu CSS rules to one (or all) of these containers but there is no telling how IE11 (or any other browser) will react to this.
Some browsers can be more tolerant towards HTML errors than others which might explain why your web page appears to be OK in some browsers but not others.
If you can fix the HTML errors on your web page, then it should be rendered with greater predictability and consistency across different browsers.
I do not know how much code on your web page is generated manually (or automatically by a theme) but trying a different theme might help.
I hope this points you in the right direction.