I am attempting to change the lock screen image using the Windows.System.UserProfile.LockScreen.SetImageStreamAsync method. On a 64 bit system, when running the application targeted at 'x86' or 'Any CPU' platforms, it works successfully the first time and then stops working. Registry logs seem to suggest that a change is being made to HKCU as opposed to HKLM when this call is made. This is visible when you check PC settings and notice that your lockscreen image in settings shows that a change has been made but this is not visible when you actually lock the system.
When switching to a target type of x64 however, this works consistently all the time.