Welcome to Android Central! When you see something like that, it usually means it's an MMS message that the phone had trouble receiving (often because your mobile data was turned off, or the mobile data reception was problematic). MMS messages are ones that include attached files (usually photos) or group texts. Make sure your mobile data is on, then see if the message comes through.
I have a galaxy note 9 running oreo 8.1. I just started having this problem on 10/26/18. None of the usual things that cause this problem have happened. Plus my phone was working perfectly fine for the past month.
Troubleshooting I've tried:
Power off, removed sim, replaced sim and powered back up