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!