Attaching a file to a "comment" is not displayed nor saved.
This issue (Comments attachments) can be replicated reliably using (3.6dev+ (Build: 20181031). Please see steps below:
1. Create a course.
2. Turn editing on.
3. Add a Wiki activity and create your first page and save (Creole or Nwiki format).
4. Go to the Wiki activity, and click the "Comments" tab.
5. Click the "Add comment" link.
6. Type a content in the text-area.
7. Attach a file in the "Attachments" area.
6. Click "Save".
Result: You will see the "text" comments only, but you will not see the file attachment.