I’ve noticed in Scrivener 3.0.1 (specifically Version: 126.96.36.199 (1274136) 64-bit - 28 Apr 2021), that page down pages way more than a page. It’s not one line over, it’s like a page more than a page. While that’s a great way of finding approximately where in your text you want to put something new, it’s not so great when you’re proof-reading existing text.
As well, it’s inconsistent. If I have 60 lines (just tested this. My page is 20 lines long on my monitor, and when I have 1 at the top, and 20 at the bottom, and pageDn, Line 60 will be on the bottom. This is quite unexpected. However, if I have 112 lines, and I pageDn, line 22 will be on the top, and line 41 on the bottom. This is clearly a bug, or a misbehaving feature. I expect Ctrl-pageDn to do strange things, but imho, pageDn itself should move exactly one page of text through the window.
Thanks for fixing this when you do, devs. I’d class this as more an annoyance than a fundamental error, but it IS annoying.