Thanks for the replies, Robin W 
So the pagination works fine on a standalone page, but if you embed it on your wordpress homepage, it’d fail.
It’s not that I have a page called “Topics,” the pagination simply uses the Topics Started slug. Even if I make a standalone page with bbp-topic-index, the pagination will still pick use Topics Started slug.
Because of this problem, I think a better solution would be to simply get rid of pagination for the shortcode, bbp-topic-index. Do you happen to know the temple file for that shortcode?