I agree with Darryl
A while back we were having similar problems with power drops. I measured the voltage, and it was down to 110.
We called FPL. They were very responsive, even assigning a customer rep.
First they changed the drop to the house from the pole to a higher gauge.
When the low voltage continued, they sent more techs over and installed a device on the panel to measure voltage over a few days.
When they looked at the graphs, it showed the voltage coming into the house was indeed fluctuating.
I was informed this had something to do with the substation, but didn't give me any real details.
A few days later, the voltage was at 120 and it has been steady since.
KP