Fallon, I had this same issue because I was following the instructions on the bottle. Don't follow those instructions! Below I will put the link to the video that helped me. In this video they say to only allow the first coat of nail polish to dry for about 15 seconds then start putting on the second coat. So you want to start applying the second coat while the first coat is still sticky. Once I did this, it worked every time! Hope that helps!
Make sure you do a first coat and let it dry then do a thick second coat on one nail at a time and use the magnet. i noticed that if you don't have your hand down on a flat surface it doesn't work well, so have you hand down on a table when your ready for your second coat & magnet.
Make sure your first coat is thin and dry. I find that to make it work well, I do one nail at a time... the second coat, you want to make a bit thick and while it's still wet, you hold the magnet over it...count to 10-15 and that's it! Good luck!