tadaaa
found the problem :P


theme customizer only changes landscape background as Theme customizer is programmed to change the landscape background.


to change the the lockscreen backgrounds follow these steps.

1- copy the path of the folder where you have the backgrounds plus there exact name with the format(.png or .jgp)

2- open filebox and go to /home/user/.config/sakya/ here you will see two .ini files ,
ignore the default one and edit the simple one by longpressing on the file , it will pop up a menu and choose edit

scroll down or pres ctrl+f and type path to background
here you will see two commands for the background.
3- now the path you have copied first .
needed to b pasted here with the name at the end.

for example

i have my wallpapers in /home/user/MyDocs/private

and the name of the wallpapers are
lockslider.png and lockslider.p.png

so the commands for the background will be .
for portrait
BackGroundImageP="/home/user/MyDocs/private/lockslider.p.png"


similarly for the landscape

BackGroundImageL="/home/user/MyDocs/private/lockslider.png"


try this and still any problem , ask freely


and yeah after making changes in the .ini save the file and the open x-terminal and type
root
killall qtlockscreen

and then check if it works .