I run Emacs 26.1 with a config of just:
(setq scroll-error-top-bottom t)
(setq scroll-preserve-screen-position 'always)
I open a long file, hit PageDown, then the Down key a few times. Point is at some position X now. I come back to the beginning of buffer by hitting PageUp twice. The point is now in the top left corner of the window. Here comes the bug: I hit PageDown and point is moved to position X, rather than to the top left corner of the portion of the buffer that was just made visible by the scrolling. The scrolling itself seems to work OK.
Cheers,
Jarosław Rzeszótko