Yeah, this is a known Windows Scriv limitation, as per @devinganger’s explanation. (On Mac page up/page down Scrivenings works as it expected.)
It is discussed in detail in this year-old thread.
If you are at all technically inclined —
Based on a suggestion from another poster, I wrote a simple script in AutoHotkey to work around this limitation, and shared it here in the same thread. The script works great. I use it every day, and this limitation (that I used to complain bitterly about 
) really isn’t an issue for me any more.
In fact, here’s the latest version of the script. When in Scrivenings, press Ctrl+PageUp/PageDown to move up or down 13 lines (half a page with my settings). Let me know if you have any questions about it.
#NoEnv ; Recommended for performance and compatibility with future AutoHotkey releases.
#Warn ; Enable warnings to assist with detecting common errors.
SendMode Input ; Recommended for new scripts due to its superior speed and reliability.
SetWorkingDir %A_ScriptDir% ; Ensures a consistent starting directory.
;--------------------------------------------------------------------------
SetTitleMatchMode, 2
#IfWinActive ahk_class Qt5156QWindowIcon
;--------------------------------------------------------------------------
^PgDn:: ; Ctrl+PageDown
Send {Down 13}
return
^PgUp:: ; Ctrl+PageUp
Send {Up 13}
return
Thankfully this is true. If it didn’t, my workaround wouldn’t work around!
Best,
Jim