The data (from the inverter) is uploaded every 5 minutes, which is essentially a snapshot of the data at that instant (random - even while a transient is happening, this is the problem). The other point which makes this a problem is that the inverter takes a few seconds to ramp back the grid power (it sees that you are exporting, and then in 2 or 3 seconds it starts charging to cancel out that export).
To put this all in an example (solar power is 0W, as to make it simple): 
  • you turn on a kettle (t=0s); 
  • in one second time, the inverter gets the message from the meter that the house is importing 3kW(t=1s, if monitoring takes a snapshot here (randomly), it looks like your system is not doing anything...but that was just an unlucky snapshot :D );
  • the inverter takes 1 second (t=2s) to ramp the discharge power to 3kW (if there is energy in battery), which results in 0W at meter connection (good time for a snapshot).
There is another instance of a bad snapshot time, when the water (in the kettle) finishes boiling: 
  • the kettle stops using power (t=0s), while the battery is still discharging at 3kW, this results in exporting 3kW; 
  • the meter detects this export (t=1s, this is an example of a bad snapshot because you are discharging precious battery energy into the grid) and communicates to the inverter; 
  • the inverter takes 1 second to ramp back the discharge (t=2s), meter power is back to 0W