How to scroll down after loading the initial messages?

Right now after loading initial messages, my collection view isn't scrolled down but it is on ~center. How can I set it to be scrolled down just after initial messages were loaded?

Start by tracing how initial messages are loaded into the collection view and how its initial scroll position is set. Reproduce the reported centered position, then verify that the view ends at the bottom immediately after the initial messages finish loading.

Written by the indexing model from the issue text.