My connection dropped for about 5min around midnight. And when it came back online, IPv6 started working.
Background- I use an Edge router lite. Have done so for practically the whole time I have had fibre 4+ years, originally with Snap, then 2deg. Around 6 months or so ago, I figured it is about time I got IPv6 working. But I couldn't get it working, and gave up. Assuming that I had made a configuration mistake with the Edge router.
Happy as this means that I actually did get my configuration correct. Although now I need to test that I have some working IPv6 firewall rules in place.