I've noticed this problem in Excel and Microsoft Edge. In Edge it appeared to be related to the zoom level; if I reset my zoom level I could use the scroll bar otherwise the 'hit box' for the scroll bar and the visual position of the scroll bar were different
In excel I get the issue of selecting a cell and it selects a different cell - this is seems to be where the scroll position of the content on the screen becomes disconnected from the scroll position of the scroll bar. This happens reliably if I have 'freeze panes' activated (e.g. I have the top row of a table frozen). With freeze panes activated scrolling with the scroll gesture on my mouse pad (two finger swipe) disconnects the content scroll position from the scroll bar position - I can see this happening; when I scroll with the mouse pad the page scrolls but the scroll bar doesn't move.
Once the scroll position of the content/page becomes disconnected from the scroll bar position the only way to 're-sync' it is to scroll the page using the scroll bar