Are you using RSync to remotely build on the Mac, or actually running the editor?
If you are using RSync, you need to go to Applications->Utilities->KeychainAccess
Once there copy the iPhone Developer certificate in the ‘login’ keychain to the ‘System’ keychain.
UE4 doesn’t use the logged in user’s keychain, so it can’t find those installed by xcode.
If you’re running the editor, you may need to open XCode and go to Xcode->Preferences then select your team and hit ‘View Details’ and hit ‘download all’ on your provisioning profiles.
While there, also make sure the iOS signing identities are valid and aren’t requesting you create or reset them.