From the spec:

bypassAutoEncryption still supports auto decryption. In cases where mongocryptd cannot analyze a query, it's still useful to provide auto decryption. Just like static program analysis cannot always prove that a runtime invariant holds, mongocryptd cannot always prove that a query will be safe with respect to encryption at runtime.

When a user sets bypassAutoEncryption then auto spawning of mongocryptd should be disabled.