What firmware version for ...
Canon 7D Mk 1, Canon 600EX-RT.
Setup is relay mode, but the latest version of the firmware rendered remote power control of the flash inoperable.
Adjusting flash power between 1/128 and 1/1 via the remote transmitter adjusts the corresponding power levels on the camera and flash correctly, but the flash itself does not adjust power. All shots are illuminated exactly the same.