After buying the streamline icon developer pack I have in a folder different icons in SVG PNG and SVG expanded formats. When I create an icomoon set based on a dozen or so of those icons (either svg or svg expanded) they appear normally in the set. But when I click on generate font for some selected icons, the screen that follows shows each icon's name but with blank icons. Clicking on the blank placeholder shows a popup with the actual icon working fine.
Uploading the resulting folder to wordpress ultimate add ons shows me the same blank icons on wordpress.
To debug I've uploaded svg and svg expanded. Played with the font download preferences. It's just when I upload my own fonts that this happens. Icomoon default icons don't have that issue when downloaded as a font.