In my experience it is t the hook temp that loosens the hook but how you handle them when removing the sprue. I have a couple of mold prone to being loose if they aren’t cut instead of breaking them off, and one is out of a pro mold. I use some single ground gate cutters that are also sold at the hobby stores. If they’re round heads you can squeeze em in a smooth jaw vise til they get a small flat spot on each side which works well for adding eyes.