Playground creates fresh WordPress instances on each page load. Refreshing the browser page discards all database changes, uploads, and modifications.
Why this happens: Playground streams WordPress directly to your browser rather than serving it from a traditional server. Each refresh starts a clean slate.
To persist your work:
Save: Enable browser storage via the "Save" button (top right, next to address bar), before refreshing the page via the browser bar.
For development: Use Playground CLI which supports persistent local storage
The dedicated refresh button inside Playground only reloads WordPress content—it preserves your PHP/WP state. The browser's refresh button (F5 or Cmd+R) destroys the entire instance.