Hey there courtmurray,
Thanks for reaching out to Apple Support Communities. I understand you’re having issues previewing Messenger messages from your iPhone lock screen. I’ll be happy to help with this.
Restart your iPhone and see if this helps at all:
Restart your iPhone, iPad, or iPod touch
Check for an update to the app itself:
Update apps or use automatic downloads
In some cases, you may need to update your iOS to get the latest update for the app itself. If you need to update, you can use the steps from these links to back up and update your iPhone:
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
If the issue continues after that, delete the app, restart your iPhone, install the app and test again
If you still have issues, reach out to the app developer for further help. This link can guide you on how to do this:
How to contact an app developer
Let us know if this helps.
Best wishes.