I'm in a similar situation, for a couple weeks now . . .
I start out the day with my hands JUST in front of the ball, with a 7i for example, and ball placement about 1 ball length fwd from center. After a while (sometimes 5 shots, sometimes 16 holes), as I address the ball initially, I'll look down at the club face expecting a square setup, but I'm closed and it feels natural. I immediately know something is wrong, but have yet to figure out what.
If I try to open the face, the odd feeling intensifies and totally screws up my entire shot, back to front, most commonly results in me smashing the club into the ground behind the ball. If I try and swing through it from the closed position, I either "goat hump" it and get a weak pull, or I actually hit it clean but get a nasty pull-hook. The only way I can get rid of the feeling is to move my hands towards the target until I'm square, not uncommon for my same 7i to have a setup with the butt of the shaft now pointing at my left pocket, 4-6 inches difference. This move allows me to manage my shot, but it also requires my backswing to be slightly different to which point I no longer have the same level of consistency, plus it just sucks.
After several failed adjustment changes (grip setup, shoulder angle, etc), it dawned on me last night that it may be my grip pressure. Again, I get the odd feeling before I make ANY move whatsoever, and I don't think it's mental becuase it can happen when I'm in the (my) zone. I tend to sweat a lot and it's been really hot lately. I normally have good grip pressure, the whole bird in the hand bit, so I think that's why I've overlooked that up until now. While in my living room last night, I noticed that if I squeeze the grip with my left hand, it closes the face. And as I get sweatier, I can't imagine that I'm not making this mistake.
Any thoughts? Guess I'm hoping someone out there has had the same issue and overcame it and has some advice to pass along. I hope to get out on the range today with some grip gel stuff I bought.