Answer:
The problem is minimal inaccuracies in both models. If the support reactions are transferred from one model to another, they are exported as "free loads" with fixed coordinates. If the coordinates do not match 100%, it may happen in edge areas that the support reactions are not considered if the corresponding objects are located slightly shifted next to the surface. The geometric relations can be quickly checked by displaying the "Full Precision" for the nodes and loads (see Image 01 and Image 02).
It is often helpful to regenerate the model and to round the nodal coordinates to six decimal places, for example. This function can be accessed using the menu "Tools → Regenerate Model" (see Image 03).
Another solution would be to move the border lines of the surfaces into which the loads are to be imported a few millimeters from the outside. This ensures that all free loads are within the surfaces to be loaded.
