John Doyle
Ansys Employee

It seems that the code cannot sort out where the stress state is on the yeild surface. 

You might have seen this already, but if not, there is a Camclay example input script documented in Section 4.11 of the R2023-R2 Material Reference Guide.  That example will solve successfully with sample properties given for a 2D plane stress, (PLANE182) under a similar displacment load.    Can you start with that example and substitute your material data in for comparison?  

I assume that all your material inputs are in consistent N-Meter (Pa) units?  You mentioned that aho=100kPa, but your INIST, appears to be in Pa.  Not sure if that might be part of the issue.