Based on what I've read so far, I would go with too warm and not enough light. In your first post you say they are 3" tall and the picture with the sharpie sort of confirms that.
I grow mine in cooler temperatures (low to mid 60's) with shop lights barely an 1" above the top leaves, and I end up with shorter, but much stockier and leafy seedlings.
From the picture they don't look unhealthy to me, just in need of a little food and a bit more light.
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