If you find an inconsistent or missing slide numbers, footer, date and time, you can reset it this way.
Go to INSERT > HEADER & FOOTER > TURN ON/OFF Slide Number
You can change as you wish. You can turn on/off all or only 'date and time' or 'footer'. However, there are some themes that are designed to work well with all.
Apply: Current slide only
Apply to All: All slides in your presentation
Don't show on title slide (Warna Cover)
If a particular slide uses 'Warna Cover' as a layout, nothing will appear.Learn more about slide layout here