I have a customer using a Cerbo GX to control their Multiplus, and since I don't personally have much experience with the Cerbo I'm at a bit of a loss as to what the fix might be.
The Multiplus rocker switch is switched on, it shows up in the Cerbo just fine and settings can be adjusted, but when turned off via the Cerbo (with rocker switch still switched on) it disappears from the Cerbo. Once that happens, the rocker switch will no longer turn it on or off until the RJ45 cable is removed.
RJ45 is in the correct port on both ends. Firmware on the Cerbo may have been updated, firmware on Multiplus has most likely not been updated. My best guess is it's a firmware conflict and updating the Multiplus may resolve it, but I'd love confirmation or alternatives/tests before he buys the MK3-USB. I don't have firmware versions handy but can get them if they will be informative.
Thank you for your time, John.