Yes, this is perfectly normal. As you progress, this feeling of not having a clue will stiil be with you, but for the pieces that are challenging/difficult/impossible. For the other pieces (that are now easy for you) you will develop a new feeling of mastery.
It works somewhat like this:
Beginner student: Does not have clue. Even the silliest piece seems impossible to play and is mastered only after great effort/time.
Intermediate student: With a little effort, sometimes with no effort at all, can tackle the easy pieces that as a beginner seemed impossible. But now he has to tackle pieces considerably more difficult and those are mastered only after great effort and time.
Advanced student: With a little effort, sometimes with no effort at all, can tackle the intermediate pieces pieces that as an intermediate student seemed impossible. The easy pieces that caused so much trouble when he was a beginner, he just wheezes through. But now he has to tackle pieces that are really difficult and those are mastered only after great effort and time.
Concert pianist: Can wheeze through anything without a sweat. That is usually when they meet Sorabji…
If I understand you correctly your way of practicing seems to be to repeat a piece from beginning to end many times, increasing speed as you go. If this is so, then your way of working on pieces is one of the most inefficient ever devised. I suggest you read Chang´s online book here:
https://members.aol.com/chang8828/contents.htmand that you explore the several threads that deal with practice in this thread:
https://pianoforum.net/smf/index.php/topic,5767.msg56133.html#msg56133(huge collection of links)

Best wishes,
Bernhard.