Model is fine before slicing, parts are added during slicing process

When slicing my model, 3d printer OS is adding parts that don’t exist, making my print unusable.

I’m trying to make lens holders for glasses.

After I slice the object, it puts a thick hard piece of plastic in the lens area:

I’ve tried every option possible including optimal rotation, and different settings including removing supports, and for whatever reason this anomaly keeps appearing. I have no idea where it’s coming from, since my model is completely clear on that part as designed.

Any help would be greatly appreciated.

Hello. We have checked the STL file and it looks like it had non-manifold edges. These problems need to be fixed before it will be possible to print the model correctly.