[OG68]

You're experiencing a loss of one of the two 120 lines in the power supply from your utility or at the meter or generator transfer switch.

Similar problem happened to my Aunt's house. Edison came out and looked and couldn't find anything wrong with the power supply and suggested an electrician inspect the house wiring.
This went on for several months. Finally total failure happened when the power pole transformer failed and the neighborhood had only a single phase power supply.

Ask your neighbors if they are experiencing the same problem. Could be a line problem or between the house meter and your transfer switch.