Weird bug that I've never noticed before

Hi everyone,

Since yesterday, I've noticed a weird bug with my iPhone 5S running iOS 8.2. The phone appears to play all alert sounds until I turn it on do not disturb mode so it won't bother me when I'm doing other things. When I take it off DND, alert sounds like the battery low warning won't play. Voiceover will announce that there is 20% remaining, but the sound won't go off. I've never had this happen before, and I've been using DND for ages. In the grand scheme of things, sounds not playing isn't a horrible thing, but because it bothers me, I turn the phone off and back on when it happens. Has anyone else noticed this? If so, what can I do about it?

Victoria