Motor's docs are generated from partly from the same sources as PyMongo's, but where PyMongo's links are internally consistent, Motor's frequently aren't. See:

https://motor.readthedocs.org/en/latest/api/motor_client.html?highlight=read%20preference#motor.MotorClient.read_preference

This is a docstring pulled from PyMongo and used to generate Motor's docs. In the original PyMongo context the link to "ReadPreference" worked, but it doesn't in Motor.

Perhaps attempt to link from Motor's docs to PyMongo's docs at api.mongodb.org when a link fails to resolve?