I am having the exact same issue! I submitted the documents for the joint sponsor a week ago, on Dec 17, and still nothing. The added the name, but there's "N/A" under the "Affidavit of Support Documents & Financial Evidence." Contacted them the third time using the public inquiry form, as the first two answers were a complete miss. Here's the second reply I got from them:
Thanks for the phone number! Will try calling them too, did they share anything about this?