In the vertical spring example, the center of mass of the "mass" part and the two points of connection of the spring were perfectly aligned with the gravity vector, thus the cylindrical joint connecting the two parts experienced no forces or torques. In this example the base is rotated 45 degrees about global X-axis, thus generating forces and torques at the cylindrical joint. These forces and torques lead to their corresponding action and reaction FEM loads which, in combination with the spring FEM loads, derive in a slightly more complex loading of both parts.
The two videos below show the assembly motion. The Earth's gravity points to global negative Y-axis. The left video shows the spring force and the cylindrical joint force and torque, all in the reference frame of the base. The video on the right shows the same vectors expressed in the reference frame of the mass.
Note how the oscillation amplitude decreases over time. In this simulation a damping constant was added to the spring.