I am performing an analysis of a simply supported beam under a central concentrated load.
When both ends are set as pinned supports, the overall displacement is symmetric, as expected.
However, when one end is pinned and the other is roller supported, the deformation becomes asymmetric, and I am having difficulty resolving this issue.

As shown in the figures, I fixed both bottom corners.
In the pin–pin case (Figure 1), the result matches the expected symmetric shape.
But in the pin–roller case (Figure 2), the upper-right corner appears to be fixed, which makes the overall deformation asymmetric.

Could anyone please advise me on how to resolve this issue?