I was playing around trying to find out what is causing this.
Seems like my app.json and appearance.json files are acting up (on Windows as well).
Disabling some snippets also ended up being re-enabled upon relaunch and themes default back to my preferred Blue Topaz (if I changed it to the Obsidian pre-built theme, for instance).
I tried simply deleting the two json files. Which prompts the question: where do the two files default back from if there aren’t any to read from the .obsidian (in my case: .pc) folder on launch? Somewhere in the Obsidian installation directory (.var/md.obsidian.Obsidian/config/Obsidian/)?
You can see in the video what’s happening through changes in GitHub Desktop:
While on Windows, I renamed the .pc folder to .obsidian, but it didn’t make any difference.