Here is what is happening:
1. “Process model client side” means that the model metadata and data will be loaded after the page loads. Nothing at all there when page loads.
2. The chatter feed is loading on page load. ANd not finding an ID from your model to bind to. So its blank. boo.
Options:
You could include Chatter in a page include. Lazy load the include and put it in a tab that the user won’t be seeing on page load. That way the page will have time to load, and process the model data aqusition client side before Chatter is even invoked.
A side note: If you’ve got any javascript that runs on page load, and uses data or metadata from the model in question - you will have similar issues.
Performance optimization is done in the ways you are attempting. Either use client side models, or page includes, or tab show actions to limit the amount of both data and metadata being retrieved from models at page load. Then load the data after showing the base page - or after a user takes some action.
