Multiple realms are configured on a proxy but one always has an 'Unknown' health check status.
The authentication health check status is mainly based on the result of the last authentication attempt made by a user against a particular realm (See 000010031). If a realm is defined but not referenced within policy (the realm may be used for testing or users have now migrated to a different realm) then no users will attempt to authenticate against the realm and therefore the health check will not know the authentication status.