How did you install the Swift plugin? Sounds like maybe it is linked with a different runtime version? Maybe revisit https://github.com/apple/swift-protobuf#building-and-installing-the-code-generator-plugin ?

@thomasvl thanks for answer. I solved this problem by reinstall protobuf via homebrew ✅

For anyone else who stumbles across this: This is currently expected behavior whenever you upgrade Xcode. Swift does not have a stable library ABI today, so upgrading Xcode will change the Swift libraries, which currently requires recompiling any Swift code.

Swift 5 is supposed to stabilize the library ABI which will stop this kind of breakage.