Can't Validate or Distribute Archive from XCode - App Store Connect Operation Error. No architectures in the binary. Lipo failed to detect any architectures in the bundle executable.

I have previously been able to upload multiple versions of our app (built in flutter) to TestFlight and the App Store. However now, seemingly randomly, I cannot even validate or distribute any archive generated in order to upload it to App Store Connect.

The error being displayed is as follows

App Store Connect Operation Error: No architectures in the binary. Lipo failed to detect any architectures in the bundle executable.

From extensive googling, I have tried the following solutions to no avail:

1. Updating to the latest XCode (Version 12.5.1)
2. Removing pod folder and re running pod install
3. Enabling bitcode - can't even build the archive as this causes other errors
4. Restarting XCode
5. Setting all frameworks as "Do not embed"

Help! I'm at a loss, and really need to get this uploaded today!