This is a great question but actually asked in the wrong order. Here's why:
Looking up or peeking as you call it is actually a reaction to you hitting the ground before you strike the ball. Your brain is very smart. After you have hit the ground once, your brain realizes what makes that happen. Once that happens and you make that move that would hit the ground your brain moves your body out of the way so you eithr don't hit the ground or take too much ground. Hence, your brain makes your body raise up and the result is you "look up" or "peek." Therefore you "peek" because you are hitting the ground.
My thought is you are making the same swing as you were earlier in the round but you were able to time the "peek" enough to poperly strike the ball. As the round goes on, we golfers tend to either get more or less confident through the round and sometimes start thinking too much about our swings. When that happens, tension comes in, causes your timing to change and then your swing errors surface. And for you that means bottoming out the club early.
So the simplest fix on the course, during a round is this. You have to get your mind out of the way and trust your swing that has been working so well. When we are thinking about your swing mechanics, you are using the left side of your brain. We play from NOT THINKING and the right side of the brain. To get there, try this simple technique. After you have picked your target, lined up, set up and are ready to pull the trigger, focus on a single spot on the ball (a dimple, a scar, the name, the number, etc.) and then say "trust it" as you start your swing. This will get your swing to perform it's best from your swing "center" in the right side of your brain.
Try it first on the practice tee and see how "little" you think about your mechanics. Now your ready to use it on the course.
It does sound like there is a swing flaw that does need attention so you may want to get that looked at.
Good Luck!