Sometimes, the PLAXIS 3D Output program does not show results for shadings or contour lines, but results are shown for e.g. iso surfaces and principal directions. This is usually caused by a deactivated Materials option (available under the Mesh menu). In that case, no element sides are drawn, and so there is no element side to draw the shadings or contour lines on.
To show results for these plots, activate this Materials option via the Mesh menu. Alternatively you can toggle the materials’ display by using CTRL+M.