Software engineering is one thing; software release engineering is another. They are mediocre at the former, and terrible at the latter.
Someone on the DJI support Facebook page says that I am OK. The "glitch" they are referring to isn't a problem with the new X5 firmware; it's the fact that the Go app claims that the aircraft needs an upgrade. The fix in today's version: it no longer says it needs an update. That's it.
But my Go app wasn't saying that, because I updated the aircraft using the Inspire 1 (non-Pro) firmware and an X3 camera. So there is an aircraft firmware update, which is currently only available in non-Pro form, and which requires an X3. So the Go app was in fact telling the truth: a newer version of your aircraft firmware exists, and you aren't running it. But since that update wasn't included in the Pro firmware package, it never got updated. Unless you used the non-Pro update and an X3.
This is an embarrassing mess. Software release engineering isn't that difficult.