Simply supported beam and Instability Type 3 issue

[rigid_joint]

I set up this simple model (symmetrical panel with uniform load and simply supported beam) and I run it.

Instability problem (as it was expected) occurred but what else could I do? I disregard it.

So far, so good. Untill somebody is taking a look a at the panel deformations.

Panel is twisting right.

(I know that I can turn the supports into fixed and add pinned releases in beam to bypass the problem but instability type 3 happens quite often and I'm not sure that finally this is a trivial problem)

[Artur.Kosakowski]

Instability problem (as it was expected) occurred but what else could I do? 

Add the RY restrain at either of supports to prevent the rotation of the model about the global Y axis as indicated in the instability warning.

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