Did those apartments have air conditioners and refrigerators running at the moment of blackout? General advice says to wait a few minutes before turning them back on. The reason is because the compressors have liquid refrigerant in their cylinders during operation. If you try to re-start the compressor too soon again after shut-off, the liquid refrigerant resists being compressed. The motor has trouble overcoming this extreme load, thus it draws much greater startup surge current.
If you wait a few minutes after loos of power, the refrigerant turns into gas which is easily compressed, and causes less startup surge through the motor. Does it take a few minutes for you to reset the breakers manually? Then that could explain why you don't have further repeats of the problem.