Thanks for reaching out to the Apple Support Communities. I understand you've had some trouble with missing messages and photos, and I have some information that may help.
If you have not already, it's always a good idea to restart your phone as described in the article below: If that doesn't help, have a look at the article below for some helpful troubleshooting steps.
Get help with missing photos - Apple Support
If Your messages or photos are still missing, you may be able to restore them from a backup. Just as a heads up, doing so will replace all Data on your phone with the data in the backup, so be sure to manually copy any information that was added since the backup was made.
If you are transferring to a new iPhone, you can move all of that data as well.
Transfer content from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support
If the behavior persists or you run into any trouble, please reach out again.