Just chiming in here 4 months after submitting my N-400. 6 weeks after filing, my I-751 was moved to a different office (NBC) for "faster" processing. My I-751 was submitted in March 2021, unfortunately to the Potomac Service Center.
Now, my I-751, if still at Potomac, should have been approved this month, and I am noticing that a lot of March 2021 applications are currently getting approved. Mine is still stuck at "transferred to another office". Average wait time to be scheduled for an interview at my local field office, going by what I'm seeing, is around 8 or so months. So, at this point, I feel like I'll likely be waiting another 4 or so months for literally anything else to happen. It's incredibly frustrating.
The advice I'd give to people here is to apply for N-400 as soon as you are able to, and not closer to when your I-751 priority date becomes current. Filing as soon as eligible will likely make things go faster than if you had not submitted the N-400, but, in my case, it seems like it has definitely slowed everything down when it comes to the I-751.