Not normal.
Usually, the agency fee of the entrusted agency is for the whole process, that is, from preparation of documents to authorization, so the response to the examination opinions that appears in the middle is included in the agency fee. Moreover, if the quality of the application documents is good, If a review opinion will not be issued, this situation is likely to be an issue with the agency's writing quality and should be resolved by them.
Of course, in a few cases the agency fee only covers process management, in which case the quality of the documents will be your responsibility.
For specific circumstances, you can check the contract.