I recall hearing both pronunciations in New York in the '50s (that's 1950s) from teachers and TV people.

Not that I heard them very often.

Wiki says Nordhoff was born in Prussia and didn't arrive in America till he was 15. If that's when he began to learn English, he probably spoke with an accent as strong as Henry Kissinger's or Arnold Schwarzenegger's.

German has no "church" sound. Maybe Nordhoff found it hard to distinguish it from "sh." Or his editor thought N was saying "chant" with an accent. Just one more consideration.

Too many imponderables here. When did the word "Schantie" first appear in German?