The GridFS spec says of the delete method for GridFS files:

If there is no such file listed in the files collection, drivers MUST raise an error. Drivers MAY attempt to delete any orphaned chunks with files_id equal to id before raising the error.

The synchronous implementation does attempt to delete orphaned chunks, while the reactive implementation does not. It's not clear whether that decision was intentional.

This causes the reactive driver to fail the new "delete when files entry does not exist and there are orphaned chunks" unified test, which asserts this behavior.