Umlauts not showing correctly in font on Windows only - Typekit

[hansottowirtz]

We're using the Apertura font from Adobe Fonts Typekit on our website and it worked great until we tried to launch our website in German (bubblydoo.de). All characters with umlauts are "glued" to the next character, but only on Windows (all browsers). On Typekit, the subset is "All characters" and we have enabled OpenType features. I'm not sure what the issue is here. Can anyone point me in the right direction? Should we consider using another font?