For what reason won't my iPhone (iOS 8) play converted voice memos?

I record a lot of voice memos, convert them in iTunes, then transfer them into my iPhone. Quite often (at least 1 out of 3 times), I'll go to play the track and it won't play. I'll have to close the Music app then reopen it to play the track. But I have to do that every time.

Please help. Like I said, I do the conversion in iTunes on my Macbook Air. I'm doing everything in the Apple universe, so for what reason is this happening?