BANDING:
If you're experiencing banding when using off camera flash, this is a result of the electronic first curtain shutter that the EOS R shoots with by default.
HOW TO CORRECT:
1.) Go to Camera Menus, Page 6, Silent LV shoot.
2.) By default, this is set to Mode 1. Change this to Disable.
3.) You're done. This will make the camera slightly louder during shooting, but it will eliminate the electronic first curtain shutter and get rid of banding when working with flashes in High Speed Sync.