Share your experience!
I used to be able to have different pictures on my lock and home screens. Now I have to have the same pictures
When you long press homescreen and choose "Wallpapers" you get preview pictures of both the Lock screen and Homescreen. You tap on the one that you want and then you can choose picture and select it. Then you are thrown back to the default screen with previews and you can hit the apply button.
If you try to set the wallpaper through google photos or google Wallpapers app (I use that one as it has some nice pictures) then you get that prompt where you want to apply it (LS, HS, Both).
Option to select home or lock screen does not work
Did you try it in Safe Mode?
For Safe Mode push the power button, choose restart, don't tap it, long press it, it will give you the choice to restart in Safe Mode.
If it does work as intented in Safe Mode then a third party app is probably obstructing the proper functioning of your device.
If it doesn't work in Safe Mode then there might be a software bug.
If the latter is the case it will be picked up by the developper and it is likely that the bug will be repaired sooner or later.
The official Sony people on this forum have a certain formula which describes this intention without making any promises. 
Isn't it like that @Jonas ?