Not a bug, the speed is simply less than 1H/s (that's because they do pbkdf-hmac2-sha256 with 10 million iterations). That means the speed is not 0, but its somewhere between 0 and 1. Hashcat however does not use floating points to show the speed but integers and that's why it's round down to 0. So, it's all fine. If you have a GTX1080 you'll have ~120 H/s.
Note that it does take 4.5 minutes on your system to test 1 password, but that's not an accurate statement. It takes 4.5 minutes to test maybe a few houndret or a few thousand passwords, that's how GPU parallelizing works. It's like with Brooks's law: While it takes one woman nine months to make one baby, nine women can't make a baby in one month.
Note that it does take 4.5 minutes on your system to test 1 password, but that's not an accurate statement. It takes 4.5 minutes to test maybe a few houndret or a few thousand passwords, that's how GPU parallelizing works. It's like with Brooks's law: While it takes one woman nine months to make one baby, nine women can't make a baby in one month.