Font rendering fine on Mac, messed up on Windows

I ran into a problem with font rendering on Windows. I'm used to a little difference in rendering between Mac and Windows, but this just made my mouth fall open. I tested the site thoroughly on Mac and I'm positive it looks just fine in Chrome, Firefox and Safari.

It looks like this on Mac browsers:

enter image description here

On Windows, it looks completely messed up in any browser (I tested Chrome, Firefox and IE):

enter image description here

I know Mac has Iowan Old Style installed by default, so I tried forcing the Mac browsers to use the webfont I generated using FontSquirrel, but that doesn't reproduce the problem on Mac.

Both browsers seem to load the same font (namely the woff version) correctly. Does anybody have any idea what this could be?

I can't post the link to the website because I don't have enough reputation, please look at the screenshots for the URL..

Thanks guys!

Solution

After some more research I found out the original (ttf) font worked perfectly fine on Windows, so it had to be FontSquirrel that caused the problems. I tried out 8 different types of settings on FontSquirrel and kept having the same issues.

After a while I decided to try a different generator and I came across Fontie: https://fontie.flowyapps.com/home

This actually solved the problem for me!