I don’t know other than Fusion was not told how to handle such situations (when the full speed of the tool is never realized in the entire design) so it comes back with a null value and then inputs “0”. I would imagine whomever programmed the post processor did not anticipate such a situation.
Someone else, I am sure, has a more concrete answer.
Just make sure in the future, there exists at least one cut line that is blue, then it will be fine. If they are all yellow, you will need to edit your gcode file.