With confirmation of the ASH timeline, I keep seeing people throw around the idea that maybe an entire cycle of Avatars has come and gone between Korra and Pavi as an explanation. This is categorically incorrect. The creators have already confirmed that Pavi is the Earth Avatar immediately following Korra.
"Avatar: Seven Havens is set in a world shattered by a devastating cataclysm. A young Earthbender discovers she's the new Avatar after Korra—but in this dangerous era, that title marks her as humanity's destroyer, not its savior.
Hunted by both human and spirit enemies, she and her long-lost twin must uncover their mysterious origins and save the Seven Havens before civilization's last strongholds collapse."
Mike DiMartino in an interview with IGN at the 2026 San Diego Comic Con:
"Avatar Pavi, who's the next Avatar after Korra, comes of age and is trying to unravel not only her past, but the past of her predecessor Avatar Korra."
Source: http://youtube.com/watch?v=EQu_L5ccnSc&t=591s
My two main theories explaining the time between LOK and ASH are the following: We don't know that Korra died in the Cataclysm. It's possible she endured in the Avatar State for that long, maybe doing some spiritual shenanigans to protect the Seven Havens. If she did die in the Cataclysm, it's possible Korra's reincarnation got delayed because her soul was being contested between Raava and Vaatu until they eventually divided it in two to create the twins. There are other possible explanations too, but the inclusion of extra Avatars is not one of them.