Ha, completely normal.
My coaches (primary and dance) and I know that I WILL have one pre-competition or pre-test meltdown where things that I can do without thinking will all of a sudden disappear. No rhyme or reason to what skills go, or when, but at some point within two weeks of a test or competition it will happen. Depending on how crazed I'm making myself, we will either push through it or move on and do something completely different (even if it means not doing a complete run through of a test or program that day).
This year it was Ten Fox. I've been doing back progressive - swing roll for years. Literally years. Then, all of a sudden, I was in tears because I could NOT do it. Then I tried harder, made it worse, then tried even harder.
Then, as magically as it all left, it reappears the next day or so. I just accept it was a bad day, relax, and move on.
I also agree that if you'd done a number of them in the session, you may not have realized that your muscles were tired and that can make a huge difference as well.