I had the same issue. To fix it, I went into the wallpapers app and used the "change wallpapers" button (instead of clicking on the lock screen, which crashes it if you do) I then chose the wallpaper I wanted and it works fine after that
Please try force stopping the app, clearing its cache and rebooting your device. If issue continues, please send us an error report to help us debug the issue. We apologize for the inconvenience and appreciate your contribution to the beta program.
