iOS 17.3, lock screen always black in one focus mode

In the "Work" focus mode, my iPhone always shows a black background for the lock screen, different to what I see when I configure it. I am using iOS 17.3, but I have had this issue with the previous releases as well.

I have three focus modes configured on my iPhone.

• "Sleep", with no background images specified
• "Sport", with a red "Color" background
• "Word", with the "Color" background you see in the attached screenshots.

This is what I see when I configure the background:

When the phone is locked, the background on the lock screen is different and is black:

The home screen has the correct background, i.e., the one I see when I configure it.

This only happens with the "Work" focus.

In the "Sport" focus mode, I have chosen a red background that is shown both on the lock and the home screens.

I have found reports of similar issues for iOS 16.

Am I doing anything wrong?