I've just replaced my old Vigor 2860 with a new 2866.  So far I've added a simple PPPoE config and little else to get connected to the internet, with the IPv6 page also set to PPP.  IPv4 is working, however IPv6 isn't.  

The WAN1 IPv6 status is showing as enabled with a link local address, but is in red so presumably isn't connected.  If I put my old router back the IPv6 starts working again.

Are there any other settings I need to change to enable IPv6?  I don't remember doing much on the old router; it just started working as soon as I set it up.  I'm using the latest 4.5.2.2_BT firmware.

I do have a vague memory that the ISP might be caching the WAN local link address and/or MAC address.

I recall that when I had this issue with my 2927ax ticking the enable RIPng protocol box seemed to give the system a kick and IPv6 started working. I could later untick that box, as it is now, and it's been working fine ever since. Worth a try?

I've tried that but it made no difference.