I had the hardest time getting Sleep++ to launch. I tried unpairing and re-pairing, uninstalling and re-installing the app. It was the only one that didn't work, and I also had 3rd party apps that did work so this stumped me completely. I was going to delete it but I read that other people had success with it on this board so I was convinced it was something with my setup.
On the other thread about 3rd party apps not launching, I saw what seemed like the totally ridiculous suggestion that I delete all of my Music(!) from my iPhone, then re-sync it all back to the phone. What in the world that had to do with my watch, and why *only* the music, made absolutely no sense to me.
So, after first backing up my iPhone to iTunes on my mac, I went to my iPhone, deleted all of the music, then tried launching Sleep++ on my watch. It would just spin for a few seconds then exit, just like before. I thought, wow, that totally did not work, and now I have to let my iPhone sync back with my iTunes overnight to get my really huge music collection back onto my iPhone (I have the option to compress my music files down to 128 AAC files since most of my on-computer music is uncompressed audio files). That happened all last night.
So on a lark, I decided to try launching Sleep++ for the first time this morning and it worked! Amazing! I have no idea exactly *when* it started working, but it was definitely NOT right after I first deleted all the music from my iPhone. At some point later, after the music was re-sync'd back things started working again. Neither my iPhone nor Watch were restarted, or unpaired the entire time. Now *that* is bizarre bug.