4. Russia attempting to throw more tension into the US relationships with Cuba and China. Historically that wouldn't be unusual at all, for Russia to screw with the US in such a way. In real terms the US is in a cold war with Russia (and has been for a decade). The US recently killed hundreds of their citizens that were acting as foreign proxy militia, in Syria; I would imagine there's all sorts of tit for tat going on between the two countries. We're into a new era of the large powers messing with each other again.
If that were the case re Russia, however, I'd have expected to see a lot more cases in China, to really push it.
Shoddy spy tech, on one side or the other, is the most likely cause imo.