Why is my lock screen not showing different pictures?

[AC Question]

Since the May 2017's update There seems to be an issue with the lock screen's ability to switch pictures every time my phone lights up to use it. It works a few times but then reverts back to display only the one same picture over and over after that. I keep programming it to choose 7 pictures (it says it can use 30). Never had an issue with this before. Anyone else having this issue?