Piston Retraction Bug

When working on my redstone circuit i found a bud working improper as it didnt retract the block.
The double piston extender in my circuit sometimes doesnt push slime blocks even when there arent any blocks attached to it. And the iron block isnt retracted.
The block should have been retracted back but it didnt.
It is a design i made for a 4 * 4 piston vault door
Pls try to fix this issue of mine.
Thank you