Identify the reading or comfort need
If Fastly switches between light and dark, check whether Appearance is set to System. A device schedule or manual system change can alter the app while that preference stays correctly saved.
Adjust the relevant control
Open Appearance and inspect the selected choice. Select a fixed Light or Dark mode if you want the app to remain in one palette regardless of device appearance.
Sound and vibration are optional feedback choices. They are separate from appearance and from the operating system's notification permissions, so a quiet-looking screen does not by itself establish silent alerts.
Check the real screen
If the preference itself does not persist and the app reports a save problem, investigate device storage rather than assuming a timer or backup issue. Appearance saving is separate from timing facts.
Keep presentation and records distinct
A different palette does not mean sessions were reset. Check History directly before taking any data-replacement action.
Fastly is a lifestyle timer and journal. These notes explain the app and offer reflection prompts. They are not medical advice or a prescribed eating schedule.