RG, at around 10:00 you have good video showing the true problem. Eratic ejection
The reason grip doesn't matter is because there is not some linear relationship of fast side equals right side, and slower slide equals straight up, and slow slide equal left ejection.
Instead, I believe it was English here on GT who pointed out the randomness of it. Something (unclear to any of us) is allowing the exracted brass to be loose and bouncing around on its way out. There has even been super slow motion video showing this. Most of the time bounce goes out to the right, but sometimes it bounces and goes out to your face. This almost like drooping an empty shell on the ground and seeing how it bounces. Most of the time it will lay down, but sometimes it will bounce in a way that stands the shell up when done.
The problem is, in theory, a bounce during ejection will by chance cause a stovepipe or other jam. But perhaps due to the overall design of the Glock, this does not seem to happen. Doesn't seem to be reported. I had 1 stovepipe in my first 20 rounds of my g4 17. Then no problems but some brass to the face in the first 200 rounds. Then very few, almost none, brass to the face in the next couple thousand rounds and current.
I have scrape marks on my brass near the open end, about the width of a pencil tip. Not dented much, but some. I have brass marks on the top right front of the ejection port (looking as you would point the gun forward), just inside the port (not on the outside of the slide).
So bouncing goes on with my gun's ejection. I would rate my ejection, and overall performance of the gun, as an A. Guess it'd be an A+ if no scrapes on the shell and no brass marks on the port.
My guess is something wore on your gun to make the ejection even more bouncy and eratic. If Win white box shells were made of abrassive material like a type of sandpaper, and you shot a couple boxes of them, and then your ejection got worse, and brass to the face started, that would make sense. I've never shot white box in mine.
While shells are not sandpaper, maybe some sort of wear has happened, and the bounce has gotten worse. Or maybe something happened to the recoil spring and slide speed changed. Grip changes slide speed, but usually not much. Maybe a big change (weakening through use, or other kind of change), in the recoil spring has changed slide speed more than grip. A light attached changes slide speed.
So either wear in the ejection parts, or a change in the slide speed, have created a bigger bounce in your ejection, and introduced even more randomness than there was before.
I get the sense the cost of the gun isn't much to you. So, leave Glock out of it. Play with the variables yourself. I challenge you in the name of backyard shooting science to see if you can fix the problem.
These are some variables to change one at a time (and then unchange to go on to the next variable). All the while shooting Lawman 124gr
-- clening the parts real good (let get dirty again to undo the change)
-- take the light off
-- new recoil spring
-- new extractor
-- new ejector.
Have faith in science, and that you can fix it. The gun is probably not possesed. The slide is probably ok, itself. The frame is probably ok. But other parts have worn and you can find out which one.