Thin walls must be avoided, both for the mechanical strength of the tool and because filling of the die can be problematic: the risk is that the powder will not correctly fill the narrow sections.
If the powder does not fill the die homogeneously, it is impossible to obtain uniform density.
Usually it is better to avoid walls with less than 1.5 mm thickness (see also image 1).
Also to avoid this kind of problems in the loading phase, it is necessary that the maximum height of a part is not more than 10 times the thickness of the narrowest section.