Set the FAB to hide read posts. The main difference to how I had it working in the past is that with this, you must use the floating action button to periodically purge this content, where as I'm sure I had it working automatically before.
I saw you posted this in another app's comments. I know Connect does 'scrolling past post marks as read', and also has 'hide read posts'. Not sure if that might be up your alley.