If this is an attack what’s the point of it. It’s not like it has any useful effects on anything either politically or militarily.
the point is probably how every US diplomat around the globe probably goes to sleep every night thinking "I hope I wake up tomorrow with without permanent brain damage"
Or are you suggesting a foreign power that wanted to cause fear would just hang around and wait and hope for symptoms to appear out of nowhere?
That said, there is the possibility that something happened in Havana and now some foreign power is reaping a long running additional "benefit" without ever attacking again.
You genuinely don't think creating paranoia for and generally antagonizing US diplomats is of any potential political or military value? If anything this creates additional stress, and demonstrates the US's total inability to defend itself from such things making it appear weak/incompetent/vulnerable to the entire world, to say the least.
Surely you're joking or feigning ignorance here, right?
It weakens recruiting for a diplomatic corps that has already seen its workforce whittled down under the leadership of Tillerson and Pompeo. Slower, lower-quality recruiting could reduce our ability to maintain influence in, and collect information from, key parts of the world. It's no secret that Cuba is an ideological beachhead used by our adversaries to hamper our foreign relations in Latin America.