After a update from Internet Explorer 11, some necessary website features are not working - many pages cannot be accessed from the menus.
IE 11 is in compatibility mode for this site, and the system was working correctly prior to the patch.
This is an issue with that release of Internet Explorer 11. It was introduced in the January 2019 patch update, then fixed in the February one:
It's the known issue listed there as "After installing this update, Internet Explorer may fail to load images with a backslash (\) in their relative source path."
The fix for Windows 10 version 1709 can be found here as an example, but in general getting the February 2019 (or or later) monthly update for the appropriate OS release will solve the problem: