Why do Facebook reels not showing or Facebook reels not loading then you should read below to find the several reasons behind the issue:
1. Your mobile data or Wi-Fi is not connected properly
2. The Facebook app has a bug or glitch
3. The device is connected to the VPN.
4. You are using an outdated version of the app
5. The Facebook server is down maybe
Source: https://getassist.net/facebook-reels-not-showing/