Answer:
The internal forces jump shortly before the support because imperfections are considered at these locations.
The imperfections from initial sway and/or precamber are applied as equivalent loads to the members. The equivalent load results in additional moments and shear forces. The moments also result in support moments from the inclination.
However, the shear forces must not generate support forces, otherwise the system is no longer in equilibrium.
The images show this effect. Image 01 shows a restrained column subject to an axial force in LC1. In LC2, a precamber is applied.
In the results of the load combination, you can see the resulting shear force from the equivalent load N * φ0: 10 * 1/282 = 0.035 kN. However, this new shear force is not an action, and thus is not considered as a support force. Therefore, the existing concentrated shear force should always be regarded as an equivalent load due to the imperfection.
Image 02 shows an inclined member with vertical loading. The inclination only results in one support moment. A horizontal support force cannot arise for reasons of equilibrium (sum of loading = sum of support reactions). If the structural system is converted into a member with equivalent loading, the same applies.
