Use one harmless event to test the same action on both clients. Note which device creates or edits it, where it appears, and how long the update takes. Keep the account and network constant when possible; otherwise list those differences as well.
Do not publish event titles, attendees, locations, or meeting links. Check whether the mobile app is showing a locally cached item that has not reached the server. A web view that lacks an event does not prove data loss if sync is still pending, but it does warrant a clear report. Check official status updates and avoid repeated edits until the current version is reconciled.
Akousa