My 3D model is printing with missing parts when sliced in Ultimaker Cura
There's a setting in Cura to Print Thin Walls. It's turned off by default, and IIRC correctly there's a good reason it's off by default. But for this item, you should turn it on. 



Update

Looking again, I see this is vertical, so I'm not sure how well this setting will help. Even if it does create the gcode to include the walls, this would be a tough print. If possible, you may want to rotate this 90° for printing, though I also see the gap on the right that would become a long bridge.