Our team likes to rely on the Activity tab of a Pull Request to see recent activity specific to a single Pull Request. When a comment is made directly on a specific file (but not on any line of the file, just on the file itself) the Activity tab shows the comment with "commented on a file but no context is available" so there is no way to know (without searching for the comment on the Overview tab) which file the comment was made on. Seems like a bug to me... the context should be available. The comment was made in the context of a specific file.
Issue #13097 duplicate