The warning:

WARNING: bad ownership on /nix/var/nix/profiles/per-user/henry, should be 1000
WARNING: bad ownership on /nix/var/nix/gcroots/per-user/henry, should be 1000

Current permissions in the profiles/per-user directory:

drwxr-xr-x 2 root root 4096 Dec 20 19:39 henry
drwxr-xr-x 2 root root 4096 Dec 20 19:57 root

Current permissions in the gcroots/per-user directory:

lrwxrwxrwx 1 root root   18 Dec 20 19:56 booted-system -> /run/booted-system
lrwxrwxrwx 1 root root   19 Dec 20 19:56 current-system -> /run/current-system
drwxrwxrwt 4 root root 4096 Dec 20 19:57 per-user
lrwxrwxrwx 1 root root   21 Dec 20 19:26 profiles -> /nix/var/nix/profiles
drwxrwxrwt 2 root root 4096 Dec 20 19:56 tmp