Ok, well, STACK only supports a subset of the maxima comands, and plot3d. and contour_plot are not supported!  Is that your difficulty?

This is mentioned in the FAQ, e.g. here
https://stack2.maths.ed.ac.uk/demo2018/question/type/stack/doc/doc.php/Authoring/Author_FAQ.md

More information is here (aimed at developers)
https://stack2.maths.ed.ac.uk/demo2018/question/type/stack/doc/doc.php/Developer/Security_map.md

If you have different Maxima images on different nodes of your cluster then chaos will almost certainly arise sooner of later!