I've never see this before in growing chilli pepper seedlings, one set of leaves have a fishtail while the remaining appear normal. This is a seed from 2021 Pepper Joes, C. Annuum "Hot Burrito" that i had left over from a few years ago
Expat living in the Netherlands from Hawaii. Growing mostly hydroponically, but upon occasion placing chilis outside when the sun makes an appearance, and the North wind stops blowing and the the rain lets up....Keith