Custom Font Icons Rendering Incorrectly in iOS9?

Has anyone else seen an issue where custom font icons in ionic are displaying the wrong icon all of a sudden when upgrading to iOS9? The icons show correctly on the browser, emulator and earlier/un-upgraded iPhones, but all of a sudden a “train” icon will start displaying as a completely unrelated icon (for example an “expand” icon) on iPhone 6 and above.

I’m using Fontastic for my custom icon font if that could be the culprit? Is there some retina icon mapping change that happened or any other thing that could be related? Any help would be appreciated as this is a real head scratcher for me…