Is it a 6to4 gateway/router? Due to the fact the hops between the client and DC have 6to4 prefixes and the client is assigned a 6to4 prefix.

Is that a separate ISATAP router?  Usually the UAG server would be the ISATAP router, but it looks like this other router is in between them.

I would guess an IPv6 firewall is in the path; this creates the additional hop in the tracert...

Now it looks like the UAG server isn't in the path.

I would guess that you also have a native IPv6 deployment in the network where your client is, since the “2002:…” - IPv6 address is assigned to the network adapter itself and not to a 6to4 tunnel adapter.

That would also explain the IPv6 address marked as “Temporary” (Statless autoconfig?) and the Site-Local IPv6 address (fec0:..).

So I’d say that you have a native IPv6 router in-between.

The client is no longer receiving a native IPv6 address and is now using Teredo/IP-HTTPS transition technologies.

I am guessing the IPv6 firewall or router than was doing RA has been removed and we are relying on IPv4 only (hence the use of transition technolgies)...