Cannot make hollow. Any Ideas.

[JoeMarkerson]

Hey everyone im pretty new to 3D printing. Im using blender to mode this model but Cura will automatically changes part of the model to not be hollow. Any Ideas on what I can try?
I tried flipping the normals in blender but that did not help.

[CollectorCNC]

I suspect you might have duplicate normals. If you can post the file, people may be able to help you diagnose.

[CAD_enthusiast]

Try SelfCad magic fix. See - YouTube