How do I set a lock screen wallpaper on the OnePlus One with the latest Android Update?
Note: This is a partial answer and is meant to solve the Lock-screen wallpaper issue only.



One way of changing the lock-screen wallpaper in CM 12 (the update for OnePlus) is: 

Go to Settings &rarr; Themes &rarr;tap the wrench icon in your current theme &rarr; scroll down to Lockscreen Wallpaper &rarr; Pick Image (choose the image) &rarr; tap Back button/key once and tap right icon to apply the custom theme. Done.