Autocorrect replacement rules, which include the pre-configured one for replacing three separate periods to a single ellipsis, are language-specific. If there are no rules installed/exist for a language used in a document, the replacement would not happen for the text marked as that language.
Your document having a history of edits in different programs, it’s difficult to tell why the language of text could be not the one you expect; but anyway, possibly you need to reset the language for selected/all text (using menu
Language), or even remove direct formatting (under
Format menu) and use styles to control the language (set on the style’s