After installed Windows 10 Insider Preview 16251.0 (rs3_release) the lock screen is a solid blue (if I change my theme color, the lock screen changes too). However, I have Windows Spotlight turned on. I've tried setting a static picture or slideshow as the background. I also confirmed that the files needed for Windows Spotlight are indeed downloaded onto my computer. It just refuses to change. Before the update the login screen showed the selected picture.