SNADI inverter randomly cycles AC output voltage

[chess-equality]

I have a SNADI 3kw inverter-charger (which I use as UPS) and it cycles its AC output voltage between low (= 204v) to high (= 220-230v) randomly throughout the day. I'm not sure what it means (flaw or part of design?) and if it does harm (to load) than good? (I'm under the impression that lower voltage means lower consumption.)