The Sync Gateway user is based on the subject claim in the token. That is the principal Id. The name and email claims in a JWT are not guaranteed to be unique and hence not used for generating the user Ud. To guarantee uniqueness of the subject claim across issuers, the sync gateway prefixes the same with the issuer Id. If you do not want the issuerId, then you must specify a user_prefix in your config.
So for instance, if your subject is “008artt9xuuFv6FWYzB8x96” and you specify the user_prefix to be “okta:”, then the user would be “okta: 008artt9xuuFv6FWYzB8x96”