I know the US desire to associate this mysterious syndrome with the sinister activities of Boris Bednov and Natasha Fatale, but I was under the impression that the puzzle had been solved more than a year ago. Perhaps the US intelligence authorities simply can't fathom there may not have been any malicious intent targeting "their"diplomats.
In any case, I'll stay with the less John LeCarre novel worthy explanations described here
https://www.sciencedaily.com/releases/2019/10/191003111753.htm
https://scitechdaily.com/scientists-find-what-caused-havana-syndrome-that-affected-diplomats-in-cuba-and-it-wasnt-sonic-weapons/
I must say though, I am sure the recent US story does make for good prime time TV and conspiracy fodder.