What was the final resolution of this? Did data come back? Does this happen periodically when apple does something?

Did you get an answer to this eventually? I'm pretty sure that testflight uses the production database.

[Update] Downloading xcode 12.5.1 removed the errors and everything built fine. So I'll just stick with that until xcode 13 is better.

I'm having the same errors (or at least very similar). I'm hoping that going back to xcode 12.5.1 https://download.developer.apple.com/Developer_Tools/Xcode_12.5.1/Xcode_12.5.1.xip

[Edit] I see that I made an answer, when it should have been a comment. Sorry about that. [/Edit] @Antonio-Reyna @gbdslmad I'm having the same error. Was fine yesterday. Stealth update of xcode to xcode 13 this morning. I didn't even know, when to build and xcode crashed to desktop. When it loaded up again it was xcode 13. Sigh. Auto updating dev tools isn't cool. I can see having to update if I wanted to support the new ios... But I don't. I'm getting these build errors mostly around my watch app/extension. In addition to  Could not read serialized diagnostics file: error("Invalid diagnostics signature") Another one I'm getting is Cannot find 'CKNotification' in scope. I think it's related, or at least because something can't build to completion. I haven't updated my m1 macair to the latest big sur update, so maybe that's it? So annoying. One thing I noticed was that it was trying to build for iPhoneOS15.0.sdk   cd /Users/aaron/Documents/Vision/Pods   export DEVELOPER_DIR\=/Applications/Xcode.app/Contents/Developer   export SDKROOT\=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS15.0.sdk Command CompileSwiftSources failed with a nonzero exit code

Getting the same error this morning. Nothing has changed in my apps database. Closing the browser helped once, then it started happening again. Have a strong feeling it's completely server side. Never seen this error before.