Hello hamishhnz,
Thank you for using Apple Support Communities. If the issue is only occurring with one specific device, we can recommend some basic steps you can try. First try restarting your iPhone to see if that helps refresh things.
Restart your iPhone - Apple Support
If restarting doesn't help, try installing any pending updates you might have available for your iPhone. This step can help resolve unexpected behaviors. Just in case, the following resource can guide you through the update process: Update your iPhone or iPad - Apple Support
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. If you don't know your passcode, learn what to do.
Feel free to let us know if that helps out. Thank you for using Apple Support Communities.