what sort of problems could be caused by lifting up in my downswing?
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First, post video if you want good input.
Second, my experience (limited and I'm a high handicapper so take it for what it's worth) standing up is a by-product of coming over the top (OTT). Simply put, your club gets so far outside the line or OTT that your body instinctively knows that something drastic has to happen to make reasonable contact with the little white ball. Work on swinging on a more inside out path to take away the necessity (reward) of standing up and your body won't need to do it any more.
Easier said than done but there it is.
Yeah similar to what Ernest said, the lifting is a compensation. The problem could be something on the backswing or just understanding how the pressure works on the downswing. One thing you know for sure, if you're slicing, the path is way too far to the left. Face angle seems fine, like you said, ball starts straight. I'd take a look at Key#2 drills to help the path.
Also you may not be lifting very much at all, not saying your buddies are lying but who knows what they're really seeing.