Erratic Zoom Demand operation

The problem: the Zoom Demand operates erratically used with a Studio Camera 4K. Instead of zooming smoothly from one end to the other it zooms a small amount then stops and won’t move anymore until the zoom rocker returns to center, then zooming a small amount is again possible. Zooming from ATEM Software Control still operates smoothly. From camera power on until the problem occurs is a variable amount of time: sometimes it is almost immediate (as soon as the remote control takes over and the tally light comes on) and sometimes it takes 5 to 30+ minutes before the problem sets in. This system has been in use for a couple of years and it used to work without this problem.
Details: Studio Camera 4K with USB connected Focus Demand and Zoom Demand. Camera connected to Studio Converter via Ethernet and POE via this connection. Studio Converter Monitor Out connected to SDI In on SDI/HDMI 3G Micro Converter; SDI Out connected to Return 1 on the Studio Converter. HDMI out of the Micro Converter goes into an ATEM Mini Extreme. Firmware/Software in all devices is up to date.
One other thing: if I disconnect the cable between the Micro Converter SDI Out and the Studio Converter Return 1 the zoom problem goes away (but of course the camera tally doesn't work).
Details: Studio Camera 4K with USB connected Focus Demand and Zoom Demand. Camera connected to Studio Converter via Ethernet and POE via this connection. Studio Converter Monitor Out connected to SDI In on SDI/HDMI 3G Micro Converter; SDI Out connected to Return 1 on the Studio Converter. HDMI out of the Micro Converter goes into an ATEM Mini Extreme. Firmware/Software in all devices is up to date.
One other thing: if I disconnect the cable between the Micro Converter SDI Out and the Studio Converter Return 1 the zoom problem goes away (but of course the camera tally doesn't work).