Rendering thai characters with tags breaks on Apple devices?

I'm trying to render Thai characters with tags wrapped around them:

So for instance: (อัน)

<i>อ</i>ัน

I want to display the character between the italics in a different color. Works fine on my Windows machine and my Android phone. But on iPhone and Mac the the superscript characters get rendered separately and not above the character in the italics.

Screenshot below testing with different tags. The one displaying correctly there has NO tags.

screenshot

Removing the tags renders correctly everywhere. Not sure at what level this issue is, but on iPhone have tried multiple browsers, FF, Chrome, Safari and on Mac as well and it seems to be display incorrectly there.