Background
While other browsers are more lenient, IE tends to interpret HTML syntax very strictly – if you have an error, it will manifest in IE where other browsers gloss over the issue.
The Problem
If you have an HTML syntax error in your menu (generally introduced via a widget or a content override), IE may seem to stop rendering the menu half way through (at the point of the error), leaving the remainder of the menu unstyled.
The most common cause is an extra closing tag (for example, an extra </li> or </ul> is a killer), an unclosed tag, or a malformed tag.
Identifying the issue
Review your content overrides and widget HTML very closely and check for errors.
Run your site through the w3c validator and work out the errors.
UberMenu will not produce any invalid markup issues on its own.
The Solution
Identify the HTML syntax error in your code and fix it.