It can be a little unnerving, but it's routine for pilots and is something they consistently train for.

There are a variety of things that can cause it to happen - windshear, traffic on the runway, approach didn't end up aligned correctly, etc. It's a ton of work for the pilots, which is why it takes a bit before they make a PA about it. The three times it's happened to me, they've made an announcement later explaining why, but perhaps in this case they were otherwise distracted/focused on setting up for the second approach.