Warning no. 335 in program QUAD

When I run analysis I receive the warning 335 in ASE “Some elements are input without normal stiffness. To bet the system stable, a stiffness times 1E-6 is assumed. Factor can be modified with GRP” QUEA."

Could this have something to do with an abnormal displacement of a plate element?

no, I think the reason is that you defined elements without normal stiffness (as the warning says).
You define this in PROG SOFiMSHC with command SAR… NRA… or within SOFiPLUS in property dialog of a structural area in tab “Geometry”.

Best regards,