One of the older leafs has brown/yellowish spots and a brown/yellowish main vein. The rest of the plant doesn't have them (at least for now). Any idea what this could be? The under side of the leaf looks fine.
It looks like a slight overwatering issue. Really those clay/tetracotta type pots aren't the best for growing cannabis. Cannabis requires more regular feeding than your typical houseplants and the clay pots actually are better at retaining moisture than what you're wanting. You can offset with a generous amount of perlite but I'd probably change pots. Strongly recommend fabric pots.
She kinda looks like a mutant but if you're feeding her I would back off the nutrients because that could be excessive nitrogen as well....the spots could be burn from nitrogen or from water being left on the leaves.