You have a couple of imports in com.mongodb.internal.connection.SaslAuthenticator.

import javax.security.auth.Subject;
import javax.security.auth.login.LoginException;

These cause a ClassNotFound exception in OSGI/karaf environments

I suspect you need to add:

'javax.security.auth.*', to the afterEvaluate clause in the core build.gradle in the

jar.manifest.attributes['Import-Package'] section