Did you take the free course on Linear Buckling?

The free course on Structural Instabilities includes a nonlinear buckling homework problem.

The geometry in the nonlinear static structural problem must be seeded with a small percentage of the buckled shape to get the structure to buckling in that way.

If you read the ANSYS Help on Pre-stressed Eigenvalue Buckling, it makes it clear that only the loads applied in the Eigenvalue Buckling are included in the solution that has a Load Multiplier.  All the loads applied in the Static Structural only serve to affect the stiffness matrix sent to the Buckling solver.  Did you read the help section on different ways to define how Pressure can be applied?  That seems relevant.