The only time I would expect the reference line not to appear with your description is when the reference is much greater than the values allowed by your response axis, which appears to be in your Axis3 definition. So you will need to show the code for Axis3 and then we can look at ways to change that to allow the reference line. It may be that the easiest approach in the long run is to modify the code that creates the actual value of &Seuilconso to also create an "nice" value for the upper limit of the Axis statement to use in a Values option.
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