One small data point I’m able to offer

My family is polish, were a few generations removed from the old country, no one really speaks more than a handful of words of polish. There’s a pretty decent amount of people with polish ancestry around us in the Philly area, and one thing that kind of sticks out to me is “kielbasa”

The pronunciation around here has been sort of twisted into something like “ku-bah-see” and it’s pretty universal around these parts, not sure how widespread that is in the rest of the country.

I think “kielbasy” is the actual Polish plural for kielbasa, so I suppose that’s part of how the pronunciation got twisted.

Bonus fun fact- there is/was a Polish organized crime group active in parts of Philly that was sometimes known as the “kielbasa posse” which rhymes when pronounced that way.

I’m also pretty sure the pronunciations of “babcia” and “dziadek” (grandmother and grandfather) in my family are more than a bit off from standard polish too, though I think that comes down to more to just us trying to say polish words with an American accent.