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:

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

James,,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.