This phenomenon has slowly snowballed over many years. It doesn't involve any notable conceptual confusion other than the milder ignorance of the relevant words, but it has further dimensions which I'll get to. People will say, in place of (the correct) 'past instances' of some kind of event, 'past incidences' of the kind of event.
A doctor is conferring with the family of a stroke victim under fifty:
He's a young man. He shouldn't be having such incidences! (Dark Water, Netflix)
I've heard people anxiously garble the somewhat difficult to enunciate 'in-ci-den-ces', or even to begin saying 'instances' only to 'correct' themselves with 'incidences'. Aside from the impropriety of usage, why think the more tortuous word is the one to use, when the easier one would do, which everyone understands? No doubt people know the term 'incidents', which denote a certain sub-class of instances. Is this mistaken use of 'incidences' a mere mispronunciation of 'incidents', or a graver sort of mistake? To speak properly of the incidence of a kind of event is not to speak of a particular case of the event, but to speak of its frequency, the rate at which it happens.
It could be because I'm getting examples mostly via Radio 4, but it may have to do with the fact that it often happens when a person is trying to sound more intellectual or more official, if not more officious, than is their wont; perhaps they have some dim association of incidences with graphs, even with inflection points.
Again, the case follows the usual pattern: An ordinary word - 'instance' - is phonetically close to a more exotic word that is it least in the same semantic ballpark - 'incidence'. Some person, unaware of the difference in meaning, uses the second for the first, and for some inscrutable reason, the virus proves to be catching.
