never had that issue before, as long as they have the same version and config

Then you are very lucky. “It worked on my machine” is a meme for a reason.

wasn’t that possible before with snapshotting (btrfs/lvm)?

I haven’t used snapshotting with those before. I guess the difference is that with nix it is done by the package manager by default, with btrfs/lvm you would have to set that up independently (please correct of this is not the case).