Hello Desert74,
It sounds like your lock screen wallpaper isn’t displaying correctly. We know how important this is for you, and you’re in the right place to find a resolution.
Are you using Focus on your iPhone? If you are, then the selected Focus might not have a wallpaper selected for that Focus.
Connect your Lock Screen to Focus
1. Go to Settings > Focus.
2. Select the Focus that you want to customize, then choose the Lock Screen.
3. Create a new Lock Screen, select an existing Lock Screen, or select multiple Lock Screens that you want to connect to this Focus.
4. Tap Done.
This info is located in this support article: Use Focus on your iPhone or iPad - Apple Support
Farewell!