I noticed a new feature which I'm hoping might be something in Gnome3 that I can turn off in LO: as of the upgrade from 22.214.171.124 to 126.96.36.199, if I click in the scroll bar, instead of paging forward (if I click below the scroll-thumb) or back one page (if I click above it), it now painfully pages forward, redrawing each page, until it reaches the point that I'd reach if I dragged the scroll-thumb to that point.
I made the mistake of doing this in a 400-page document with many comments (i.e., interactivity is very laggy and slow anyway), a distance of about 200 pages forward. Not only did this single mouse click lock up all LO windows while the next 10 mins passed as it struggled to the new point in the document, but it interacted awfully with the desktop: I couldn't click to focus on any desktop item; the most I could do was use Alt-tab to bring different windows to focus.
If you must jump to the scroll position, rather than scroll by 1 page as LO used to, at a mouse click, please, I beg you, don't do it incrementally one page at a time with a redraw for each. It's torture!
Oh, I also realised it makes an important interaction ability impossible now: previously, you could select a long range of text, and then click in the scrollbar to view back to the beginning or to the end, as you wished. (You can't do so by using Page-Up or Page-Down keys, as that loses the current selection and shifts the insertion point.)
And with the new behaviour of clicking in the scrollbar, it's impossible to easily move to the start or the end of the selection, in a long document: it's too imprecise for accurate positioning, and thus too hit-or-miss.
As you mentioned Gnome3, are you running LibO with GTK3?
Launch methods for gtk2 and 3:
Sorry, I can no longer reproduce the problem after I uninstalled libreoffice-gtk3 to get rid of the low-usability Open dialog it brought to LO. I understand that that change was due to Gnome3, not LO (and there's another workaround, too: to select the use of LO dialogs rather than let the desktop environment provide them: good!)
I believe it was at that point that the awful scrolling behaviour ended, but I'm sorry, I can't be sure.
GTK3 + LibreOffice is still experimental and should not be enabled by default.
Another scrollbar bug is bug 98726
Created attachment 123662 [details]
works fine for me with the 700+ file format specification
Double checked in a 5-2 and no sign of this problem. Maybe it was a temporary period while gtk3 was experimental where there was some smooth scrolling bodge in place.
I've not had it happen again for months, so I'm perfectly happy for this to be resolved.