Ok, so I just learned about the disagreement between HE and cogent. What is bugging me is that HE seems to find a route, but I believe there is no route back, so connections time out before falling back to IPv4.
Here (https://www.agwa.name/blog/post/working_around_the_he_cogent_ipv6_peering_dispute) somebody found a solution to this on Linux, by rejecting/disabling those routes. Is there a similar way to do this on Windows? I found a way to manually route to my loopback interface, but since this fails it tries to then use the default route - which times out - and then falls back to IPv4. I have not been able to find a way to reject/disable a route on Windows (10 Prof). Is there a solution at all?
Ok, so after digging around I couldn't find a way. Maybe it has to do with the way Windows NT desktop versions handle fallback routes. What did work was setting outbound rules in the Windows firewall dropping connections to the unwanted IPv6-networks.