Applying multiple signatures on XFA form in Acrobat Pro?

Apologies if this question has been answered before, but I spent some time looking and didn't see anything directly on point. We're working with an XFA form in Acrobat Pro. The form is intended to be signed by up to 6 or 7 different individuals, each of whom plays a different role up the "food chain" in the approval process. The first person to sign can apply a digital signature in Acrobat Pro, but after that no one else can sign or add information to other fields. Our tech department has (supposedly) confirmed that the form is not set to lock once signed.

Any idea what might be going on here? Is there a correct way--within Acrobat Pro rather than having to go to the web--to configure a PDF form for multiple signatures? Because the form is XFA, I can't examine the existing properties for each of the signature fields.

thanks in advance for any help!