Ref T12616. When you "Delete" a comment from the preview, we try to delete the comment on screen too.
It may or may not be present on screen: if you just added it it's usually visible. However, you might also have hidden the file it contains or it could be on an older diff in a file which is no longer present in the current diff.
After updates in T12616, we could only find the comment if you'd previously interacted with it for some reason. Update this code to be able to find all inlines present in the document.