Pg Up and Pg Dn started to work chaotically

Recently, the behavior of Page Up and Page Down keys changed. So far, I could use them to navigate within a zoomed page, because it jumped only one screen's distance up and down (based on the zoom level, I could jump two, three, ten or even more times till I reached the bottom or the top of the page). Now, sometimes it works the same way, sometimes it jumps directly to the end (Pg Dn) or to the top (Pg Up) of the page, regardless of the zoom level. In these cases, I cannot use Pg Up and Pg Dn to navigate, and always have to search where I was in the text. It's quite frustrating, and makes work slower.

The strange thing is that the behavior can change unpredictably. I was reading a 219-page pdf document, there was no problem in the first 45 pages, after it, the keys started to behave abnormally. (Parallelly I opened several smaller, 2-10 page long documents, and closed them after comparing them.) Settings were not changed, of course.

The view is set to single-side view, the version number of Acrobat Reader is: 2023.003.20284.

Could someone help me, please?

Thank you!