Looked through glibc changes from 2.27 (shipped with core) to 2.29 (version on the host). I have not noticed anthing potentially breaking around locale-archive handling.
However, based on a hunch, I started tweaking /etc/nsswitch.conf since it does influence resolving hostnames, triggers dynamically loading nss backends and potentially talks to the host systemd/resolved.
The segfault went away when I edited /etc/nsswitch.conf like this:
...
# hosts: files mymachines myhostname resolve [!UNAVAIL=return] dns
hosts: files myhostname resolve [!UNAVAIL=return] dns
networks: files
...
Looks like there’s a potential issue with nss-mymachines compatibility. Potentially nss-resolve and nss-myhostname (also part of system) could be an issue too, but so far only mymachines seems to be breaking things.