Hey man what strain is that? You would need to give a bit more infos but it looks like a revegging plant, not really revegging but it is havving problem, it could some light leaks where it is growing or way too much nitrogen on some strain will create this pattern also on some strains i have seen it before on very indica strains. But if you see a 1 bladed leaf like this in the middle of flowering something hapened with the lights a lot of the time.
Good luck