Hi @klum,
The preview feature and toolbar are not being phased out, and should work as planned. We'll try and figure this out 
Have you given a look at this post: Troubleshooting: Content Previews? It covers common issues with Previews and you'd want to rule out everything on there first. Has the draft you're trying to preview been published before?
If nothing on there helps, could you record a Jam of this behavior? If you don't want to share it publicly, you can send the link to me in a private message.