Flat clasps with gemstones or designs on the "top" always flip over, because of gravity. I really don't understand why clasp designers don't add some weight or volume to the back of the clasp to prevent this. Or make the clasp double sided. Well, I do know. It makes the clasp double in price.
I replaced most of my clasps with Orbit clasps or big hooks. Easier to use. They sit well at the back of the neck. And the orbit clasps look good (look like links) if worn in the front. Plus, I can link necklaces together for longer strands when they all have orbit clasps.
I also have some spherical clasps. They look the best, and it doesn't matter if they roll around. But they are too fiddly for me to do, so I only put them on ropes, so I don't have to actually undo them to put the strand on.
Another way to prevent a clasp from flipping is to use a multi-strand clasp, and put it on a double or triple strand necklace. But single strands will always flip.