UIScrollView shift down 44px (equal navigation bar height) right after dismiss modal view controller

UIScrollView shift down 44px (equal navigation bar height) right after
dismiss modal view controller

I have an UIViewController with a navigation bar. My UIScrollView which
contains a list of UIButtons is added programmatically. I set the
scrollview's frame and contentSize according to the button list count.
It works perfectly until there is a modal view is showed and dismissed.
After the modal view is dismissed, the button list in the scrollview is
shifted down 44px (equal navigation bar height). When I try removing the
navigation bar, everything work correctly.
I searched in the below questions but they aren't my case. Contents of
UIScrollView shifted after dismissing ModalViewController Contents of
UIScrollView shifted after dismissing ModalViewController
Thank you