Problems creating an ABBA pattern

I’m trying to use Tynker to create ABBA patterns from Maths. Hopefully you can see the code here -
In the third last line, I’d like to use Switch to Costume 1. If I do, the pattern breaks. If I use “Next costume”, it works.

Why? How can that be explained to a kid?

Just a stab in the dark but did you define what Costume 1 is?