I encountered a similar bug, and even having a fallback font did not fix the issue. The Montserrat font was loading fine so the fallback was never loaded.
As it turned out, using the CSS rule font-feature-settings caused this particular font to stop displaying altogether in IE10 and IE11 on Windows 7. (Though it would probably cause similar issues for other fonts).
The fix was to disable the low-level font tweaks of font-feature-settings
, using the IE vendor-specific prefix:
/* Fix for IE10 and IE11 Montserrat font display issues. */
p {
-ms-font-feature-settings: normal;
}
If possible, it's probably best to avoid font-feature-settings
altogether. OR make sure you have testing regimen in place to test the various IE browser versions on each Windows OS. Especially since font rendering is not just a browser feature, but also a function of the underlying OS.