Hustle Opt-In Will Not Submit - FIRST_NAME must be provided

When a member attempts to submit their information on a Hustle opt-in, the following JS error is generated: https://goo.gl/cU2XiC

Full conflict test has been performed with no improvement. The Hustle error log states the following:

James,james@example.com,FIRST_NAME must be provided - Please enter a value,2017-05-11

As you can see, the first name is provided.

More information, including access, in chat log.