If you cannot find a solution, try downgrading your STP to when you saw L2. I don't know if you are getting STP through your broker or directly. Whichever way, ask them for a slightly older executable. If STP autoupdates, I doubt there's anything you can do about it. Ask other users if they are getting L2. If you are using Windows 10, you might want to tweak it so your i3 runs faster. See if W10 is blocking your datafeed but I doubt it. Good Luck.
I get STP through my broker. I can't downgrade to the previous version, unfortunately. My broker is saying my I3 is the reason I can't see it. And that I can't see LULD after resumption of halts, which I think is crazy. I don't see anything blocking my datafeed.
I can't really do anymore from here. If your broker has a forum, ask other users if they are also having L2 problems. Otherwise, you might have to bite the bullet and buy a newer laptop. If your broker doesn't have a forum, ask other users of your broker here at Elite Trader if they are having L2 problems.