Sun GTIL inverter issue?

Hi, I have been using two 1000w Sun GTIL for about 3 years without problem. Recently I got some more panels so I switched the output limiting function on to test it out before summer comes when I will need to limit the inverter. My issue is the wattage on the inverters display jumps around? It will be 300w max then dip to 17w then rise again? I have the limiter set to 900w. Both inverters do this then settle down for a while and start again. Has anyone else had this issue?