I have a feeling that it is something in the software that is causing the lags/lockups. I have a theory that maybe it's something to do with tournament lobbies and the main tournament lobby and the way they are refreshed. I tried opening lots of big MTT lobbies alongside a game and there was some performance hit. But when I close all MTT lobbies AND ensure that the main PokerStars lobby is not showing the tournament list, ie. showing something that doesn't update as often like the Zoom poker tab, it performs more smoothly.
Maybe it's worth giving that a try if you're experiencing big problems.
And I think maybe the reason lag issues are affecting everyone to different degrees is dependent on what computer system they are running and whether it can cope as well with the lockups from the software.
That's my stab at trying to solve this anyway
* So in summary, maybe try closing all tournament lobbies and ensuring the main Stars lobby is not displaying the MTT schedule.