When we copy host addresses to the container we copy all their attributes.  Mostly, that's what we want, but this includes the IFA_CACHEINFO attribute which governs address expiry.

This means that if the addresses on the host have finite lifetime - which is typical if they're managed by DHCP rather than statically, then the container also gets addresses with finite lifetime.  However the container lacks the DHCP client (or whatever) that's maintaining address on the host, so once the lifetime expires (typically some hours to days later) it will simply lost connectivity.