This sounds very similar to my case.
After the interview, we had been approved, passport stamp etc, but nothing happened after that. Also, at that time, my online account had no updates at all (since last August).
We needed to make an infopass appointment to straighten things out.
We were indeed approved, but a final computer step had not been completed - literally a button "click" was not done.
Anyway, the issue was resolved - they had to order the file back, complete the AOS step on the computer, and then the processing and card production in Missouri could go ahead.
Whatever the reason for the delay in your case, I would definitely make an infopass appointment to find out what the problem is. It may be something as simple as a step not completed.