This also seems to be an issue with the Cotton Candy Flower. I was able to make it initially (and still am able to craft it) for the event tasks. However, while I am able to sell anything I craft, if I see it in someone's Side Shop it is locked to level 75 (and I am still only at level 72).
I have never had it asked for in an order--whether plane, train, truck, balloon, or anything else, other than for the event--so it is not an issue for me as of yet. Still, it does seem strange that it is both locked and unlocked.
At this point, perhaps the level it can be unlocked should just be lowered to 70 or 71, to coincide with being able to purchase Blueberry Bushes and craft Blueberry Sugar (which is one of the ingredients needed for the Cotton Candy Flower).