SOLVED: It turns out that this issue was caused by a quirk of DJI's unlocking license. When I left the Dallas (DFW) area my Mavic had an unlocking license turned on for all of the DFW area where I usually fly. When I got to eastern Pennsylvania where I am now, I tried to take off but kept getting a message that I was in a No Fly Zone and couldn't take off.
While trying to problem-solve this I went into the Unlocking Licenses section of the Go app and decided to turn off the active license for the Mavic for the DFW area. Once I did that, and tried to take off again, all was good. See attached image.
So... lesson learned: Turning ON an unlocking license apparently restricts you to flying ONLY in that area. In my opinion, this is counter-intuitive and confusing. Why would this disable all other areas outside my unlocked area? My assumption would be that all non-restricted airspace that I can normally fly in would still be active, along with the unlocked areas. And instead of a message saying I was in a No Fly Zone (which was not true), perhaps DJI could use a different message telling me to check my unlocking licenses. Just makes sense to me.
Although this was a minor inconvenience in this case, it could have been a major problem if I was shooting commercially at a client's location and didn't know why this was happening, I would have had to scrub the shoot.
Hopefully this will be helpful to some of you in similar cases.
