Hello 
I think I’ve got a semi clear repro…
It seems it happens for me when the loader slider is in the still loading state with spinner shown when opening a topic.
Seems somehow it re-render the topic (maybe) when the cloaked-posts loads and those height added to it and jumps to the wrong place.. not sure 
Repro:
- Looking for a not too small topic with some unread replies.
- Set the browser network to Slow 3G (just to makes sure to show the spinner on loading)
- Open the topic
Result: