I've seen right then U instead of left, straight then U then right instead of left, right then U then right instead of straight, and lots of variations of around the block routing. One that I encounter myself about once/week is a straight then U then right instead of left.
Whenever I encounter this, traffic is heavy or has been recently, but generally hasn't been heavy for more than 1/2 hour. Waze is seeing that the left turn is slow, but has no idea that the U-turn it's asking me to make will be even worse. Depending on the light cycle, I can sometimes make the left before I could have gone straight, but that's just timing when I reach the intersection.
Orange County, CA, USA, Samsung Galaxy S3, Android 4.3