Mine curl like that when the nighttime temps get below 50F.

This happened in the middle of summer when temps were in the 70's. Not worried though will get all the seeds I need this year.

That's strange. They usually love temps in the 70's and 80's. Glad you got seeds, though.

Hello WMC1, I grow Rosa Sinesis type tropical Hibiscus and get this happening yearly when a bug we call, the Chain bug, arrives and sets about 'stinging' buds. If they don't fall, they open up deformed like yours.

You may have another bug that does this or have the Chain Bug himself. You will recognize them as they go around in pairs or more attached to each other by their tails. Each bug is about 1 to 1.5 cm long - narrow type brown bugs. They tend to drop to the ground rather than fly off when disturbed.
Another suspect is the Rutherglen Bug, or name like that spelling. He is very small, below 3mm and black and whitish in colour, but would say the Chain bug is best bet.
Good luck.
Regards, Brian Kerr.