Alex, much thanks. I forgot to reply and just ran into this issue again – you’re on the mark. Even just toggling this while running nixos-rebuild will prevent the issue.
I wonder if this also will lead me to fix another long standing issue I’ve been having with linux (LXC) containers, where for some reason the user ids aren’t being mapped to container specific uids (like mapping the container’s root to 1000000) but that’s off topic for this conversation.