We just also started seeing this same error within the past 24 hours. (today is Sept 10). Our minimum target has been iOS 12.0. What is the new minimum target that TestFlight/ASC checks for upon upload?

Moving my CrashLytics phase to last worked for me! thanks! In my case it was second to last. The last build phase I had was an "Embed App Extension" for a push notification service, which is now before the Crashlytics phase.