I just ran snap changes and saw the the core snap was "Refresh"ed and the multipass snap was "Auto-refresh"ed:
ID Status Spawn Ready Summary
186 Done 2018-02-21T19:37:31Z 2018-02-21T19:37:56Z Refresh snap "core"
187 Done 2018-02-22T15:30:09Z 2018-02-22T15:34:22Z Auto-refresh snap "multipass"
What’s the difference here?
The Refresh snap "core" message is created to describe the change when the you do, for example, snap refresh (or also snap refresh core foo bar; anything other than just one).
If you’d done snap refresh core, the message you’d see would be Refresh "core" snap.
The Auto-refresh snap … message comes from snapd itself, doing a periodic refresh and finding it can refresh something.
There’s a fourth one, but there’s a bug that makes it look like the first one, which is what you’re seeing here. That’s the fallback systemd timer prodding systemd in case the internal timer got stuck.