That is quite baffling! I have no idea why one would work and not the other. Without being able to reproduce it myself, all I can do is suggest ways to narrow down what might be causing it:
Try reversing the order of the shortcodes, and adding text before and after them.
Retype the shortcodes to be sure there is no stray control character, and that the double quotes are really plain ASCII double quotes.
Disable any other plugins you have installed.
Change the theme.
In the webforms admin area, change the identifier from “test” to something else.
If you have the expertise to edit the database directly, you could look at what is stored in the ewz… tables and see if anything seems odd.