I am also experiencing an error with the 3D topology optimization of the Ysplitter example. I am running the Python codes from within the Lumerical FDTD environment on 2022 R2.3 version and I have looked for a solution on the forum but have not found any. The error refers to a part of the design in the example, which is called "initial guess" which is the environment we indicate in the code for the topology optimization to happen. I ran them in the Lumerical FDTD environment without changing any of the codes. After the lsf file creates the geometry, I run the Python code for 3D optimization. At this stage, I do not start from a previously optimized 2D file but rather from scratch. Please see here the links to the files that I am using:

For the lsf script file, I use:

For the Python code, I use:

I'd appreciate your help with this as I have exhausted all possible solutions and have not yet been able to get the code to work. Please see the screenshot attached. Thank you!