I could be wrong, it’s not really a diagnosis just a guess from experience. I did have it before only one time, on one plant from seed. I smoke and grow tobacco so could’ve been a leading cause. I just kept it from touching the other plants and always sterilize any razors or scissors you’re using between different plants. If the leaf feels almost bubbly to the touch and the surface is a bit raised where it’s visible on the leaf then I would say that’s what it is. Send an update if it changes please.
Thank you