I was in the same situation and even tried to request that our case be transferred to another service center from Potomac but USCIS said they can't do it. Unfortunately you just have to wait. When you end up calling USCIS ask them when your case was last touched (looked at/reviewed). That might be a sign that there's some activity with your case and it's not just sitting there collecting dust. You might also want to ask whether your case has been assigned to an adjudication officer. When they told me this about our case it was approved about a week later. Good luck!
Unfortunately I think this is common many of us get Nebraska as an online status and even on the NOA1 but end up at Potomac with no explanation or notification. I’ve seen it a lot on here and no one is notified. You have to message uscis yourself to check, which sucks. I’m sorry this happened.
