As I have already reported, I could still live with the fact that by adding end elements to a curve (arrows, points..etc.) I was able to work around the problem (1.8.1.604Beta) with truncated ends. But with this version even this is no longer possible and in addition the "Add" function causes errors again!
I have added an AD file with the document history, I hope you can see and reproduce the problem!
AD_1.8.1.611_Beta_expand_stroke.mp4
AD_1.8.1.611_Beta_expand_stroke.afdesign