Apparently snaps are also sandboxed between versions of the same application. My very first experience of snaps was Vuze getting updated overnight and all my configuration and torrents just vanising.

I ended up rolling back the version (to restore everything that disappeared) and, upon discovering snaps are designed to never be able to lock a version number, shot it in the head by killing the daemon and chmod'ing its executables to not be executable.

I assume Vuze's snap was misconfigured, but it really turned me off of them and I've since decided to stick to nix instead of snap whenever I can.