In a very new Xcode 9.4.1 project, the problem was that my subfile deployment target was set to platform :ios, '11.0' while my iOS deployment target for the project was set to 10.3.
This caused the generated Pods project to target iOS 11.0 (only supported on 64-bit arm64 devices), but since my main project is 10.3 and includes armv7 devices, this does not work when archiving the Release assembly after the Release build builds inactive architectures by nature (unless you only support iOS 11 devices).
The fix is simply to change the deployment target of the subfile according to your main project, in my case it is platform :ios, '10.3' . After that, run pod update and the Pods project should be restored. Launch Xcode, perform a cleanup, and you can start the archiving process.
Chee-yi
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