I am currently stuck on strumming (specifically up-strums). Has anyone else gotten stuck or have suggestions on how to move past?

Every time the pick hits the low E string on an up-strum, it slightly moves, until after about the 3 strums it faces 90 degrees with the point facing down the neck.

Every...single...time

I've tried thin picks, and thick picks, I've tried adjusting how I hold the pick, I've stopped and started, and tried to retrain everything I can think of...every time I up-strum the pick moves and will rotate down the neck. I have to be doing something wrong technically.

I've stopped any GT lessons involving strumming because it's so frustrating, and I can't seem to find a solution or reason. I've got 200 hours of practice time, and still cannot get a strum going with up-strums and it makes no sense.

[u][/u]