Please refer to the "Patreon Shop Launch" post over on Patreon as well as the "Update & Page Accessibility" post here on itch.
As far as I understand it, as it currently stands, the game still awaits its manual review. Until then, downloading the game from itch seems to be a game of chance (apparently the current version is supposed to be downloadable from your library if you've purchased any v1.0 or later version. But several comments have pointed out that this doesn't seem to work...)
Therefore it's only available on Patreon right now. Since there's apparently no way for Patreon to know wether you've already purchased the game on itch or not, you'd need to purchase it on Patreon again. Siren is aware that this affects a lot of people but unfortunately there's nothing really they could do about this problem.
(However, once you've purchased the game on Patreon, future updates will be free, just as they were here on itch.)