Discordant shape features


I am testing pyradiomic feature repeatability of all seven feature classes(Shape, First-order and 5 Texture features) between different CT images. The phantom i use is a CIRS electron density phantom with 16 solid inserts, therefore, I compare the feature value extracted from insert #1-16 of image 1 with the features extracted from corresponding inserts of image 2

I am using an identical method for segmentation ie creating a 13mm radius cylindrical volume 15mm in length(5x3mm slice) for all inserts in my multi-electron density phantom. The issue i have is no shape feature reaches stability which i have specified at 85% CCC.

I am unsure why shape features are discordant, any help would be greatly appreciated

best wishes,