Format the card itself or put another card with just OS and see if the behavior changes. I get this behavior sometimes and formatting my card has brought me back from it in the past when flashing eMMC with a backup did not. The card is being read since Hekate is booting from it, I'm thinking something else on the card is causing an issue. Our situations may be different as my Switch will enter RCM on its own and try to boot. Since the battery can't be disconnected until after the SD reader that gets problematic for repair and has caused me this issue before.