On my sg4 suddenly the set as menu in stock gallery has disabled the lock screen options

[AC Question]

When I open a photo in stock gallery, then open the actions menu, then select set as, the lock screen and lock/home screen options are marked with the red slashed - through symbol meaning the action is not allowed. I've had this phone several years and have never seen this before. I was able to work around the issue, but what's the deal?