Why is POWEReasy showing a warning?
Your site has observed high variation in voltage in a 24 hour period. If there are significant fall and rise in voltages it does have an adverse effect on electrical appliances. Indian electricity act requires low voltage supply to be maintained within a +/- 6% range.
When do you need to fix this and why?
This condition is coming from your supply. Is it advised that you protect your expensive and critical devices by installing suitable voltage regulation devices.