There is a very nasty setting which will prevent the YN622N-TX and YN685N from being used together.
When the autofocus assist is enabled on the YN622N TTL will not work. Therefore, setting YN622 to TTL and YN685 to R.Slave will not fire the flash. You can verify if autofocus assist is one by checking if "AF-ILL" is depicted at the bottom right of the YN622 screen. It can be turned of by pressing the "AF/SS" button.
You can only use autofocus assist if the YN685 is in manual mode or the YN622 is in manual mode.
Why does it not work?
Maybe Yongnuo is afraid that the autofocus assist interferes with the light metering system of the camera, which is used for TTL. However, I verified that the flash does work in TTL mode when the on-camera autofocus assist is enabled. So it must technically be possible to use the YN622 with autofocus assist and TTL. Therefore I think this is a bug in the system.