I stopped wearing my Apple Watch because of this issue. Apple is going downhill.
Why? Just fix it. You probably don't even need to spend like 3 hours going through all possible solutions, like me, if you just try deleting the music first. Now, I don't even have the slowness issue some are talking about. 90% of the time, all my apps load in under 5 seconds, even when they're refreshing.
Just days after deleting and reloading music the issue is back. So tonight I deleted all music and rebooted phone and watch...apps work again. Reloaded music. Apps still work. Something after that causes the problem to recur. Reboot, syncing...who knows. Frustrating.
EDIT: so one more thing to add. After getting things up and running and all my music back, I confirmed that the process will survive a reboot of the phone but NOT the watch. As soon as I restarted the watch the same series of apps that wouldn't run, failed again.![]()
You have to back up the phone and set it up as a new iPhone.