Inverter that will "stop" production when the battery is charged

Hi, I have an issue with a Zonergy VENUS C inverter (6kw panels, 10 kw batteries) and the people who sold me this can't seem to solve this.

Basically the sistem will work just fine in the night, when my house electric needs are been satisfied by 10kw batteries + inverter.
In the morning the sun will rise... the inverter will start producing and feeding into the batteries. It will also read correctly the value from the load. 
Then at like 10AM, the batteries will be fully charged, and the inverter will "stop": the display (and the app) will show 0 watts from solar, 100% battery charge, 0 watts from load (not true) and no tie to grid.

The sistem doesn't have a meter, but only a CT that is clamped with the arrow in the correct direction (according to manual => Grid) on 2 wires: one that goes from inverter to grid and another that goes from grid to load.
I live in Italy, if this is a relevant info.

The vendor said that maybe my grid is sending me some inconsistent tension and this is making the inverter go into protection... but now they have updated the firmware and all is good: this doesn't seem to be the case since in a day I am producing 4-5 kw... when i should be producing more like 14-19kw with this sun...

Thank you in advance to anybody that can help me solve this conundrum!

(I Forgot to say: the inverter is not in in a "off grid mode": this behaviour is consistent in all modality... one called "fullyfedtogrid" and the other one "Selfconsumption" where it should export when the needs of the house has been satisfied... but still... 0 export)