[Hummingbird] Hummingbird is changing font

I've struggled quite a bit with Hummingbird changing the font on my website. With HB disabled there are no problems. With HB enabled and after running the performance test, the webpage doesn't load the correct font. If I clear the cache in the minification dashboard, it's solved but only to return after a short while. Both your support heroes and I have tried numerous things, for instance excluding various items in the minification dashboard, but to no help.
I use WPML to translate my site into two languages, and sometimes we can make it work in one language but not the other.
Are there any other magic tricks available that we can try?
The problem doesn't look the same in different browsers.
Best wishes
Peter M.