Hey there A-f114E,
Thanks for getting back to us with that information. We'd like to take some steps to test the software on your device to see if that might be what is causing this behavior.
Before we get too far in to that, let's also check to see how much available storage is on your device. Please navigate to Settings > General > iPhone Storage. Let us know if your storage is full, or if you have some available space.
If you do have a good amount of available storage left, the next step would be to make sure you have a recent back up of your information. You can check when the last backup was made by going to Settings > [your name] > iCloud > iCloud Backup. It should show you when your last backup was made at the bottom of that screen. If you don't have a recent backup, you can tap on "Back Up Now" to create one.
How to back up your iPhone, iPad, and iPod touch
After that is done, the next step would be to connect your iPhone to a computer to restore your device to factory settings. Once it is set up as a "new" device, we would want to test to see if this same behavior happens with your apps and messages. Take a look at the steps here for some guidance on doing that:
Restore your iPhone, iPad, or iPod to factory settings
If the behavior does not persist while you have it set up in its factory state, you can then restore your backup file on to the iPhone:
Restore your iPhone, iPad, or iPod touch from a backup
Doing these steps will isolate the issue to being either something within the iOS software that was installed, or to a possible physical device problem and help us determine the next best steps to take.
Let us know if you have any questions or run in to any issues on this.
Regards.