This is maybe an esoteric scenario that doesn't have a clever idiom, but I feel like I can almost recall one but can't quite.
So the scenario would be along the lines of bringing something up that is uncomfortable that is not especially informative because everyone is already aware. For example, if a kitchen sink were dripping, and someone made a point of "informing" everyone every hour or so "man, that kitchen sink sure is dripping. I think it might be slightly worse than when I brought it up an hour ago." Or another example, if a relative were quite ill and has been for the last two years, and your cousin calls every week or two and says "I saw grandma this weekend. She looks terrible. I don't know how much longer she has."
The idea being that the person saying it might have ulterior motives for bringing it up, or just doesn't grasp that bringing it up as though things have gotten worse when they are really just as bad as before is more frustrating or upsetting than useful.
The first phrase that crossed my mind was "whistling past the graveyard", but apparently that has almost the opposite connotation, as it means to act cheerful when things are obviously dire.
I feel like a lot of reporting these days has this sort of vibe, where headlines wail about how much worse things are than they were yesterday when they reported nearly the same bad news, so I'm grasping for a turn of phrase that describes this sort of thing.
Best Answer
Thanks, Cpt. Obvious!
Loosely related to the expounder Mr. Exposition, a TV trope that provides infodumps or expounds the plot. An agitator or lamentor.
Additionally, AYKB (As you know, Bob), discussed here (Info dumps, Soap-boxing, Lecturing).
Sometimes described as the Turkey City Lexicon, or a FAQ Literator.
Loosely related concepts are: perverbs or Wellerisms (making fun of established clichés and proverbs by showing that they are wrong in certain situations, often when taken literally) and Tom Swifties (a speaker attribution that puns on the quoted statement).