Hey buddy,
I've never seen anything quite like this..
But at first glance, it could be a nitrogen deficiency or a lack of another nutrient.
What I recommend is to do a flush and if you think it's okay, give your plant a dose of nutrients.
But since it's practically the end of the grow, you don't have to worry too much.
The plant even looks nice like this xD
Congrats on the grow and hugs!