There are a number of reasons this may happen. First, it is important that when you receive an edited manuscript from us, you must check for any comments by the editors seeking further clarification, asking questions, or pointing out missing information/unclear sentences. These should be addressed before the work is submitted for publication.
Any amendments you make to an edited manuscript must be checked by us before you submit the paper to the journal, or else this risks introducing new mistakes to the text, which may prompt negative comments during peer review.
It is also possible that your paper's reviewer(s) is not a native English speaker, and is thus possibly not qualified to critique the language in your manuscript. If you are concerned about comments you have received about language, please send them to us and we can help to resolve the situation.