Hello xsirx,
This appears to be happening on your Lock Screen wallpaper. We'll need some additional information to suggest a solution. Let's isolate this further.
Have you test a simple restart yet? If not, that would solve simple issues: Restart your iPhone - Apple Support
What happens if you use another wallpaper? Learn how to change wallpapers here: Change the wallpaper on your iPhone - Apple Support Does this occur with the emoji wallpaper, for example?
Does the behavior change if you switch this to a different photo? Or select a different color for the text in this wallpaper?
Let us know, take care.