Please reply with an image of your geometry and make sure the Global coordinate triad is visible in the image. Add an image of the Loads and Supports in another image. You can get that by clicking on the Static Structural branch.
A good diagnostic for finding the source of the problem is in Workbench, drag a Modal analysis out and drop it on the Model cell of the Static Structural analysis. Then in Mechanical, drag any supports from Static Structural and drop them into the Modal branch. Then solve the Modal analysis. Add Total Deformation plots to look at the animation of each mode. You might see what is moving the the global Y direction that is not properly constrained.