See PHI2029. An install reports that Jupyter notebook diffs render all inline comments on line 1 if the raw source file is a single line (for example, because the JSON has been minified).
This is likely caused by internal logic clamping the display line to the number of lines in the file.
When you are viewing a change under engine X, and comments made under engine Y are present, they are not handled specially.
- From T13534.