So I had a similar issue and was very excited to try out your theory. In my case, it didn’t end up being a solution. I still needed to set an item.range for kebab-cased completions, or all but the last fragment wouldn’t be replaced. Also, I’m not conditionally setting this range only when more than the current “word” needs to be replaced, and completions still work fine when the range is set.
My current working theory for my case is that I was trying to helpfully format completions with JSON punctuation (e.g., ", :), and Nova was suppressing it when item.insertText began with one of those characters. I’d really love some clarification from Panic on why provided completions might not be displayed.