Inquire if your ISP applies CGNAT for its customers?
I believe CGNAT doesnt work well with recursive resolvers like Unbound:
Some users were able to opt out of this CGNAT after contacting their ISP:
EDIT: When run below one, do you see an IP starting with 100.x.x.x which confirms CGNAT being applied?
traceroute -n 8.8.8.8
From the wiki:
The allocated address block is 100.64.0.0/10, i.e. IP addresses from 100.64.0.0 to 100.127.255.255.