catwoman1704,
Thanks for getting back to us.
Have you updated to 16.0.2 yet? We'd recommend being on the latest iOS to rule this out as being related.
Do you use Messages in iCloud? This setting is in Settings > [Your Name] > iCloud > Messages. Once enabled, this will sync your Messages everywhere you are signed in. If you have another device signed in, could you Messages have been deleted there? This would delete them on your iPhone.
You can read more about the feature here: Use Messages in iCloud.
If that doesn't explain the issue, please reach out to Apple Support for a deeper dive.
Have a fantastic day!