how to delete a 'ghost' signing certificate (Xcode 13.2.1)

In my keychain, I have one Developer ID Application certificate, with a private key, for my Team. In Xcode's Accounts/Manage Certificates dialog, there are three Developer ID Application certificates, two of which have a red 'x' badge and the status 'missing private key'. I can right click on any of those three entries and my only enabled choice is "Export". Email creator or Delete are disabled. Why? In my Team's account, there are indeed three Developer ID Application certificates, with different expiration dates, but I only have the private key for one of them. By choosing Manual signing, I can choose a specific certificate from my keychain, but Xcode 13.2.1 tells me that this certificate is missing its private key - but I can see that private key in my keychain!