This issue has been happening to me sporadically since Apple renewed one of the intermediary CAs involved in developer certs. At first I was fixing it by removing and regenerating certificates, it turns out the simplest way to fix the problem is to just reboot, and everything works again.
Putting this here as an option for people to try before they start destroying their work environment / needlessly complicating their keychain settings where a reboot may also 'fix' things for you (at least for a couple of weeks at a time if you never shutdown/reboot otherwise).
Topic:
Developer Tools & Services
SubTopic:
Xcode
Tags: