Most often this is because of custom capabilities which are not yet supported in the new app.
There’s quite a bit of discussion of this in the following thread, although it’s also mixed in with discussion of other features of the new platform that wouldn’t apply to hub – connected devices, so just be prepared for that.
Custom Capability and CLI Developer Preview
@jkp or @orangebucket might be able to add any other relevant threads. Because none of these kind of conversations work well with my voice reader, I don’t follow them very closely.