Guilin Sun
Ansys Employee

With very little information, it is hard to say what is the cause. Please refer the example: https://optics.ansys.com/hc/en-us/articles/1500006203341-GDSII-Export-Automation

I would suggest to test the case with fewer geometry and see if it works.  GDSII supports limited number of points, depending on the version. Here are a few posts that might be helpful:

Lumerical FDTD gds export vertices limit

如何导出结构组?