Code reviews are usually done asynchronously and in writing through a code review tool. This is usually out of convenience, to enable remote code reviews, and to allow multiple people to review the same code change. But when is it time to stop using the tool—however good it might be—and start talking face to face about the code?
Good code reviews leave as many comments and questions as are needed. If the revision does not address all of them, they will note those as well. When the conversation gets into a long back-and-forth, reviewers will try to switch to talking to the author in-person instead of burning more time using the code review tool.
Better code reviews will proactively reach out to the person making the change after they do a first pass on the code and have lots of comments and questions. These people have learned that they save a lot of time, misunderstandings, and hard feelings this way. The fact that there are many comments on the code indicates that there is likely some misunderstanding on either side. These kinds of misunderstandings are easier identified and resolved by talking things through.