The issue of plot lines disappearing when saving a figure as a vector image in MATLAB can sometimes be related to the renderer being used. MATLAB has different renderers (painters, zbuffer, and opengl), and sometimes switching the renderer can resolve such issues.
Renderer Setting: The set(gcf, 'Renderer', 'painters') command sets the renderer to 'painters'. This renderer is typically used for vector graphics and can help preserve plot lines and other graphical elements when saving as vector images.
If the problem persists, you can also try using the exportgraphics function (https://www.mathworks.com/help/matlab/ref/exportgraphics.html), which is a newer and more versatile function for exporting graphics in MATLAB. The 'ContentType', 'vector' option ensures that the output is a vector graphic.
