I assembled a three-phase system with:
Two Multiplus II 48/5000 / 70-50
One Multiplus II GX 48/5000 / 70-50
I don't know why, after the configuration for 3 phases, I have VE.Bus error 3 all the time. I checked the cables dozens of times. I updated the firmware to version 2623498 on all inverters. Also the internal Cerbo in this one inverter has been updated. I disconnected everything except the battery. Despite this, the system still won't work. I suspect you can't mix the regular Multiplus II and the built-in GX.