Disabling CSS didn't work. Instead of a submit button, I got a spinning loading wheel, or whatever you want to call it.
I tried all of the text widgets both with CSS on and off.
I tried the [sp-signup] shortcode, and it gave me a signup form with just an email, the no list error, and the spinning wheel.
I tried the shortcode with first name, last name, etc. and it gave me a signup form with the no list error, email entry box, and the spinning wheel.
I tried the html from the form button, and it gave me the correct signup form but still no submit button (that's how it is on the site currently if you want to check it).