That’s strange. The first thing I would try is getting two 1/2-20 (I think that’s the thread) nuts and tighten them to each other on the stud and use the outer one to turn the stud out. That way if it rounds the edges it’s just the nut and you can figure something else out without rounding off the stud itself.
I use PB Blaster penetrating oil for things like that. If you can find a 6pt box end in that size it will give you good grip. Also, like @whiplash473 said, bind 2 properly sized nuts and turn it from the front - that way you can use an impact.