I just finished "The Spy in Moscow Station" which talks about these signals. Although this isn't a direct response to your point about mortality, an interesting

I just finished "The Spy in Moscow Station" which talks about these signals. Although this isn't a direct response to your point about mortality, an interesting feature of the Moscow (Microwave) Signal is that it -- considered as a surveillance threat, rather than a health threat -- also received a lot of the same skepticism I'm seeing in this thread. The TL;DR is that various agencies strongly resisted attempts to dig into why the USSR was directing microwaves at the embassy, despite the fact that the USSR had already been caught placing microwave-powered listening devices inside the building. The book describes an argument between State, CIA and NSA in which the former two mostly wanted to ignore the signals. The belief was (1) that no technology had been demonstrated that these signals could exploit, and (2) even after the NSA cooked up some examples, people refused to believe that the USSR was sophisticated enough to exploit them. (I won't spoil the book by giving away the resolution.) I'm not offering this as any kind of proof that the current batch of Havana syndrome cases is real: just pointing out that while "we've never seen it before so it probably doesn't exist" can be a reasonable heuristic in day-to-day life, it's not necessarily a great one in the world of spying.