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Prattler is the word that comes to mind.
The person can be said to suffer from verbal diarrhea The fact or habit of talking too much: was it necessary to have the narrator exhibit verbal diarrhea throughout the entire picture? [Oxford Dictionaries Online] Similarly logorrhea excessive, uncontrollable, or incoherent talkativeness [Collins] And, by extension, they might be called a ...
I might call them a "chatterbox". An extremely talkative person. The definition on Urban Dictionary might not be as academic, but it certainly matches your description. Someone who never shuts the hell up. They keep blabbering about random crap that makes no sense
Hard to think of a good noun option. Blabbermouth. Motormouth. Windbag. They all sound somewhat dated. Although I do like windbag. Adjectives that might help: "prattling," "filterless," and "windy." Or you could get metaphorical. In college, who we nicknamed a kid who did that "Filibuster" -- it stuck.
Sometimes it helps to change the word order of a puzzling and/or archaic sentence when you're trying to work out the exact significance of its individual elements. (This is particularly so with poetry, where the poet may have moved a word from its expected position in a sentence in order to accommodate the dictates of metre and scansion.) Updating the ...
If the person usually ends up off topic, and you want to express that point, I'd consider using digressive (although it seems to be more commonly used to describe conversations/text rather than people); as Collins has it: digressing or given to digression As Hellion notes below, serial digressor, or perhaps just digressor, would work if you're looking ...
It's an informal neologism, but oversharer is an increasingly commonly used descriptor, as a quick google search will show.
I like verbally incontinent, as Mark Darcy described Bridget Jones.
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