The Donmeh, a secretive offshoot of the Sabbatean movement that outwardly converted to another faith while privately keeping its own.
In the engine's read, it's an example of a group hiding what it really is for a very long time.
The mechanism is a false public conversion kept up in secret, with roughly 360 years of documented deep-cover persistence.
It shows how a hidden identity can survive quietly across generations without being detected.