If you have an older version of Xcode installed you will need to manually update the Apple Worldwide Developer Relations Intermediate Certificate. Certificate and more info in links below.
https://www.apple.com/certificateauthority/AppleWWDRCAG3.cer
https://developer.apple.com/support/wwdr-intermediate-certificate/
I faced this issue today and had to update the intermediate certificate, delete all old certificates related to app signing in keychain, regenerate certificates on the developer site and make new provisioning profile. Then signing worked again. This should only be an issue for you once your existing certificates expire and you want to make new builds again.