Hi
Try ->
On the iPhone hold down the Sleep/Wake Button and Home button together until the Apple Logo shows. Then On seeing this Apple Logo release both buttons ,and the iPhone will reset , which has been known to clear most glitches.
If this does not remedy the issue then make a back up to iTunes and or iCloud and restore.
If this does not remedy the fault if you have a local store create a Genius Bar appointment via this official link from Apple
https://www.apple.com/uk/retail/geniusbar/ -> I suggest making an appointment because if they are busy it's possible they will not be able to see you and run a diagnostic on the iPhone.
Current Phone >
Samsung Galaxy s²⁴ Ultra 512gb.