@yueliu30
Please carry your receipt, any other notices issued by USCIS, your I-20s, job offer letters etc. I carried everything with me, like even my passport and I-94.
Good luck. Ask for an ineterim EAD. They calim that they do not issue it anymore, but doesn't hurt to ask. Also ask the timeline for the expedited EAD.
Not to discourage you but this is the letter I received today in mail.
The processing of your case has been delayed. A check of your records establishes that your case is not ready for decision. as the required security checks remain pending.
Until the security checks have been completed we cannot move forward on your case. These security checks are required to be completed on all applicants who apply for the immigration benefits you are seeking. We will make every effort to make a decision on this case as soon as the security checks are complete. If you do not receive a decision or other notice of action from us within 6 months of this letter, please contact the National Customer Service Center.
Hope you have better luck.