When I first heard of the Havana cases, the descriptions of the effects reminded me of the complaints of residents near IWTs (industrial wind turbines) only more serious. These have often been suggested to be due to infrasound. https://littlefield.co/the-psychoacoustic-effect-of-infrasonic-sonic-and-ultrasonic-frequencies-within-non-lethal-cf05e1fd8673
However, what makes ultrasonic perhaps unlikely is the targeted nature of the effects... one would assume that if exposure was to something like ultrasound, the effects would be very widespread as opposed to just a building (or a floor of a building).