I can verify that it's Snap Store specific because I uninstalled the Snap Store version and installed the PPA version, and I no longer have the issue.
Basically, when I close Spotify when using the Snap Store version, I think there's a configuration setting that doesn't get persisted. This is because when I open Spotify back up, the volume returns to max. My ears kept getting blasted every time I booted up my computer because I kept forgetting the volume hadn't gotten persisted.
With the PPA version, I don't have this issue. This leads me to believe it's to do with the confinement of the Snap Store. Maybe it's an