Now my host lxdbr0 route looks exactly like yours (I don’t have linkdown in the line like you though). Thanks for pointing me in the right direction @tomp!
The most helpful Network Engineer award goes to you! 
I’d like to get edit rights please to our tutorial so I can correct the mistakes in there: Getting universally routable IPv6 Addresses for your Linux Containers on Ubuntu 18.04 with LXD 4.0 on a VPS