OAuth authentication error in RHOCP 4: user cannot be claimed by identity as it is already mapped

Issue

• Login to the platform with a certain valid user fails with:

  Error from server (InternalError): Internal error occurred: unexpected response: 500
  

• After setting debug log level in authentication operator we can see:

  "Error: user <user> cannot be claimed by identity <identity>:<user> because it is already mapped to <identity2>: 
  <user>"
  

• Oauth login fails for a user when the same login account is available from two different identity providers.