Large white message notification window on the lock screen
I have a iPhone 6S with iOS 12.1.3
When new messages arrive and if the phone is locked there will be alerts on the lock screen. These used to be individual, grey and rectangular boxes. When there are no messages nothing will be on the lock screen. This behaviour changed today abruptly. Now when I reach the lock screen a large, white empty boxy is displayed. If there are any new messages, the alerts for these are shown inside this large box. I do not know if they are really inside the box or are just overlapping it.
I am including the image of this white box below. How to get rid of this? I have not changed the OS or the notification settings recently.
I use fingerprint scanning. So if I use the correct finger, this window is displayed only for a second before the Home screen in showed. I used a wrong finger to keep the phone in the lock screen and show this.
Thanks
iPhone 6s, iOS 12