I got the same update this morning, which was as a result of calling the uscis for change of address on my vawa case after my approval notice was sent to my old address.

oh OK, and congrats on ur approval but I didn't call them for anything, another thing again, it says the notice had been sent back to uscis because it couldn't be delivered

Did you make an inquiries on your case? if you did it might be as a result of that. Thank you Wishing you luck in your uscis journey.

nope I didn't inquire I'll just have to wait I guess

With Vawa, I think it's the most mysterious uscis I would advise you not to over-stress about it.