Strange behavior of slide to type keyboard

At some point in the last year, the slide to type keyboard on my iPhone X has started to always insert the text "and's" when I enter the word "and" - every time, and no matter how carefully I enter the word. This doesn't happen with regular tap typing.

I've mostly developed a reflexive habit of fixing it back to "and" from "and's" but I'd really rather not have to. Is this a bug in the software? It can't be intended, since "and's" is not a word and would never be used in regular writing.