Empty diagram - embedded sub process (collapsed)

I’m using embedded sub process (collapsed) on my process diagram. During process execution in web app (flowable-ui/admin) when I choose action “Show process diagram” main process is presented but when I clicked on rectangle of my embeded sub process on it - unfortunately an empty page is presented.
I have no idea what I’m doing wrong, maybe someone has already had this problem?
I’m using flowable version 6.8.0