As shown in the picture below, there are no Net stats, but seeing the realtime data it should be a lot higher then the 0.02kWh it says it used from the grid 
Anyone has an idea how this can be caused ?
Did you try to reload the page?
yes i did, even tried just now again to be really sure i did
it does show some usage, but WAY to low for my real usage.
I have exactly same problem some days. There aro also no data in DESS stats. Works again after Cerbo restart.