All other devices stream (locally) just fine without stuttering, I don't have access to the server outside my home network (intentionally).
The appleTV streams just fine, I just can't change audio track on that, which mostly impact the kids because they still have limited English skills.
I don't have audio sync issues at all. I have issues with appleTV using the wrong audio track when I select something different than the default. E.g. if I select Danish, it shows that it's using the Danish track but it's actually playing something else like Finnish or Swedish. This behaviour is only on the appleTV and no other devices.