I see that you're having an issue with your notifications and the text expanding past the banner. I can see your concern and I'd be happy to take a look at this with you.
Let's start by going into your settings and toggling off your notifications, then restarting the iPhone and then turn notifications back on and test to see if the issue remains. Go to Settings > Notifications > Messages.
If after trying these steps if the issue still remains, reply back with the answers to the following questions.
1. Which version of software are you currently using?
2. When did you first notice this happening?
3. Does it only happen with Messages? Or with notifications from all apps?
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Have a great day!