@leocg It has been confirmed on two computers (new profile, Windows 10), so I am willing to share any info if required to debug.
I have yet to have a look at a portable installation, but it does not occur often enough to be a real nuisance for me, and refreshing the pages log me back in whenever it happens anyway.
YouTube is the most obvious with the autoplay switch turning itself on as well as cinema mode (enlarged player) turning itself off, but once again, I rarely use YouTube myself, so it does not bother me as much as it might seem.