First of all, to make sure that we are on the same page, we support ie11 only and there is no support for older versions.
The Internet Explorer version 11 has few problems rendering some Flex properties. You can read about the problems and possible workaround here.
The most problematic one is when you add value without units for the flex properties. For example, the
auto will not render correctly in IE 11.
Try to check your header bar container and other elements and make sure that there is no
auto value, instead of that you can use
The Pro header and footer Builders are heavily dependent on the flexbox. Unfortunately, there is no robust way to separate a header to show only for the IE 11 browser.