I have checked the model of the "Air Fresh Top" more than once and it is manifold. You can see in the photo from the link above that it prints with the entire section missing.
The slicers skip adding a layer in the area indicated in the image below. How do I get it to add a layer?
There is nothing wrong with the slicers; it's the model that has a minor design error.
When the model is cut in half it's easier to see the mistake.
The slicer tries to fix that issue with an overhang wall (blue), but evidently it's not very stable.
I printed this "Air Fresh Top" (with a 0.6 mm nozzle)...
(Please don't mind that single loop of spaghetti.)
... but the ridge came off very easily. I'm not exactly sure what the purpose of that ridge even is.
