Good feeling sociological nonsense. Usually unrelated to reality in any fashion and about as useful as tits on a chicken.
Kumbya is most often found in the pseudo-science fields of sociology, psychology and education. Rampant in academics that haven't been in the field. These are universally shocked when the warm fuzzy theories don't pan out.
It gets passed on by such academics to the next generation of young students without the experience to know better. Those that get into field work soon abandon it, or the field work. Older persons (Over 30) entering such fields see Kumbya for the crap it is. But the professor (frequently younger than you) will fail you if you call them on it.
The most pernicious are those that hang onto the Kumbya in spite of knowing it is useless, usually social workers that know they are useless.
Kumbya is named for the rather pleasant and repetitive spiritual folksong that is a campfire favorite, used to bring a nondenominational feel goodness to the group for no practical reason.