Same issue on Xcode 12.4 (12D4e). Occurs a couple minutes after releasing the app version to external testers. My application is using Cocoapods. Was able to resolve the "Invalid Swift Support" error by re-installing my pods (ie. pod deintegrate - pod install). Still seems very random, hopefully this may work for someone else too.
radmob_dw
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Also currently experiencing this issue. Waiting on response from Apple Developer Program Support.