Experiencing this too. It worked once (I had to set my router to 2.4gz) and the symbol cache sync took about 30 minutes which feels like a bug in and of itself. Now I'm not able to run builds on that watch despite trying every fix mentioned here and on forum posts online I'm getting this error now Previous preparation error: A connection to this device could not be established.; The device rejected the Bluetooth connection attempt. This makes making an Apple Watch app almost impossible.