I'm having the same issue with my fritz.box
But I think mine does not have the ipv6 settings since I might have disabled all ipv6 functions...
Benjiir, where is that setting located.. Or should be located?
Is there any other thing I could do?
Oh and it is not on every page.. Only on some.. And some work faster others slower..
Without they are usually all fast (cable 400mbit)