There is a bit of inconsistency in the setup because you drop your butt sometimes in the squeeze, but generally you are setting up with the bar a touch behind mid foot. Make sure it is over your shoelace knots and then bring your shins to touch the bar. This will likely have your knees flush with the front of your arms (not behind the front). Then I would slow your squeeze down a bit and keep your butt locked in place as you go. And yes, stand up all the way while still looking at your spot on the floor.
Your grip is definitely being lost. Are you using chalk? If not, try to (you can get liquid chalk if you need to be sneaky). If you already are, you may have taken jumps that were a bit too much for your grip to catch up to. You can certainly switch to a hook grip, but this will be painful in the beginning and usually people need to practice it at lighter weights for some time before using it in working weights. Thus, a reset to a lighter weight and smaller (5lb) jumps might be needed if chalk is not the issue.