The first couple of times I tried the app I got the Apple Watch version of the endless spinning pinwheel and had to reboot my watch. I finally got the app into Sleep Tracking mode and yet it didnt collect any data.
After three days of persistent use it did give me data for the third night. But then the data for the fourth night was corrupt and not useful.
Very buggy and not ready for prime time.
ottawasabi about Zleeper, v1.2