can't sync iPhone 7 playlist to apple watch

I have had this problem that occurs more often than not when trying to sync with my Apple Watch. I have the watch paired with the iPhone and charging. The iphone connected to BT and WiFi. I select Music in the Apple Watch app (I have it set to the max of 2GB of music) and then pick a playlist from my iPhone that is 520MB in size. Most of the time, the "sync pending" will show up and never progress past this. On rare occasions, it has synced music to the watch. When I try to update the playlist and sync again, it often hangs on "sync pending". It has also erased the playlist from the watch on several occasions, or stated the sync was complete but then only about 10% of the songs could be played on the watch and the remainder were dark colored and couldn't be accessed. I've tried unpairing and repairing the watch from the phone on numerous occasions. I've hard rebooted both watch and phone on numerous occasions. I upgraded the watch from watch OS 1 to 2 and then to 3 without any measurable change. I recently purchased both an iPhone 7 and Apple Watch 2 and find the exact same issue persists with totally different hardware.

I see others have similar issues but not certain why this is so persistent across operating systems and device upgrades. I've read Apple's support on this issue and following all recommended procedures. Anyone else had this issue and found a fix?