Impossible to say why a delay. You can call to enquire or make an Infopass appointment.
Samuel Ouya Maina, Esq. 415.391.6612 email@example.com Law Offices of S. Ouya Maina, PC 332 Pine Street, Suite 707 San Francisco, CA 94104
Make an InfoPass appointment with the USCIS.
(213) 394-4554 x0 Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.
You should make an Info Pass appointment and determine where the card is being sent. If possible and under your circumstances, CIS may give you a temporary stamp in your passport for proof of status. You may want to retain counsel and have the card sent to your lawyer to ensure its delivery.