Symptoms
WIF10201: No valid key mapping found for securityToken: 'System.IdentityModel.Tokens.X509SecurityToken' and issuer: 'https://ststest.CLIENTSSITE/adfs/services/trust'.
Diagnoses
After applying a rollup with new AD FS tokens, the error above occurs when going to Designer.
Resolution
Updated the ADSFS thumbprint with the new thumbprint in the ClaimsIssuer table of the K2 database to resolve the issue.