Hello!
That's not expected behavior, so try taking the following steps which may help with this: restart your iPhone, make sure it is up to date, close the affected app (Messages) then reopen it, and make sure all apps are updated.
Restart your iPhone
“1. Press and hold either volume button and the side button until the power-off slider appears.
2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo."
Update your iPhone or iPad
“1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. If you see more than one software update option available, choose the one that you want to install.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now."
Close an app on your iPhone or iPod touch
“1. From the Home Screen, swipe up from the bottom of the screen and pause in the middle of the screen.
2. Swipe right or left to find the app that you want to close.
3. Swipe up on the app's preview to close the app."
How to manually update apps on your Apple device
“1. Open the App Store.
2. Tap your profile icon at the top of the screen.
3. Scroll to see pending updates and release notes. Tap Update next to an app to update only that app, or tap Update All."
In addition, try deleting the full message thread and starting a new one as that may also resolve this issue.
We hope this helps. Let us know if we can assist with anything else at all. Take care.
