This message has no content
MY iPhone keeps saying "this message has no content" where it use to show a sample of emails in mail. It just recently started doing this. Also some messages will show jubberish.
If it says that when the message has an attachment or a photo, but no text, then that's normal behavior.
Otherwise, Try these standard troubleshooting steps.
Reset: hold down the Home and Power buttons until you see the Apple logo (10-20 seconds).
If this doesn't help, you might need to Restore your iPhone: https://support.apple.com/en-us/HT204184
If your backup is to iTunes, make sure it's an encrypted backup.