Firebase crash console asking for UUID of a build

Question

I am trying to get crash reports working on my ios app. I am getting an error message in the Firebase Crash dashboard that says

Upload symbol file to symbolicate future stack traces for UUID 69696969-7F8H-567E-1ABCD-FAKEID123

I have checked every binary on my machine, and not a single one of them has this UUID. So where is this UUID coming from? I put a fake one in the example above obviously, but how can Firebase be asking for this UUID if it doesn't exist?

Note that this is a test crash. I am calling

FIRCrashMessage("Hey man, you crashed.")
fatalError() 

in my app. The build is one I've downloaded from iTunes connect via TestFlight. Is Apple creating a binary that I don't have a dSYM file for? I have bitcode disabled.

I also verified that the run script is working. If I click "Symbol Files", to the right of "Dashboard" on the Firebase Crash Reporting tab I have lots of dSYM files uploaded to the Firebase Crash service, but none match the UUID of the binary I've downloaded from TestFlight.