Notebook not working

I'm trying out Kotlin Notebook for the first time, and having a hard time getting anything working.

For example , I can add a new Markdown cell & type in some Markdown.  If I click the “code” button to create a new code cell, all the text in my Markdown cell immediately disappears.  If I click back into the Markdown cell, it doesn't let me type anything.

I'm new to Jupyter notebooks so it's possible I'm doing something wrong.  But even trying to do the simple things in the JetBrains video doesn't work.  I suspect that there's just some incompatibility somewhere…

I'm running the latest version of IntelliJ, Ultimate Edition, and just installed the Notebook plugin.