I have issues with this sometimes. However, you have failed to tell us where the icons are not appearing. You left us in the dark .
Are you sure you are using the correct code that IcoMoon provides? E.g. \e606 or whatever in the content property of :before / :after? Just shooting in the dark .
Now, where do you believe that the IcoMoon files are being stored live? Please grab me the direct link to an IcoMoon file .
The CSS for it is being called; just not linking up with your IcoMoon file. So there is a discrepancy to where the font files aren’t being properly called.