Focus motor works great but when I connect the Sony A7III to the RSS splitter, the LED light on the focus wheel turns solid yellow and focus control becomes erratic.  
On the A7III, parameters are set as follows:

- Focus mode is set to M
- USB connection is set to PC remote
- Control with smartphone is OFF

Never mind, I had the USB-C to USB-C camera cable improperly connected.  Elbow plug has to be connected to RSS splitter and straight plug goes to camera.