Hey folks
for what it’s worth, I thought I’d report an issue we’ve been facing during our first day of class with fresh students, with a newly installed software stack that includes jupyter lab.
I’ve been receiving numerous reports of “jumping scrolls”, i.e. people being “teleported” elsewhere in their notebook, or not able to scroll up to the previous cell; this having been particularly experienced by teachers apparently, who use smaller displays (in pixels) when mirroring with projection devices, and who also tend to make text larger for legibility
After a bit a messing about, it appears that the issue vanishes when the notebook windowing mode is set to defer instead of full
I figured it out incidentally, because I was not experiencing the issue myself under similar conditions, and then I recollected that in my env I had set windowing mode to ‘defer’ a few months back, because it interfered rather badly with a - totally unrelated - extension of mine
but the symptoms were resonating with what I had seen at the time, i.e. annoying and inexplicable teleportations towards another location in the notebook at apparently random times
Then one teacher mentioned it seemed to be related with cells that are higher than the viewport, and it clicked …
hopefully this can help others facing the same issue
(and TBH I have to say the move to using full windowing mode by default has been IMHO a bit of a big leap in the void, as that technology does not seem quite ripe yet, imho again; but that’s another discussion entirely 
)