I love how it seems like you get gated if you fall behind. Blue posts on catching up on renown are about as vague a description of a solution as I have seen so far in this game. They even punt it to Wowhead for an answer:
https://us.forums.blizzard.com/en/wow/t/renown-catchup/764734/3
It seems to be once again 100% random if you actually get to move up or now.