Most likely same as: Code signing is required for product type 'Application' in SDK
Can you please follow this guide https://devcenter.bitrise.io/ios/code-signing/#collect-the-required-files-with-codesigndoc and upload ALL the files collected/exported by codesigndoc ? That should help.
If it would not, please copy paste the related build’s bitrise.io URL so that we can look into it.