Didn’t plugging in an iPad or IPhone to power used to Wake a MacBook as well as initiate iTunes Sync? I ask because mine do not (I thought they did previously) and wonder if this is related to the sleep wake issue.
The Mac needs to be awake to perform on demand tasks.
I set mine to never sleep. And then let the screen and hard drives shut down when unused. But the actual cpu needs to be awake.
If iTunes is open on the computer, and you checked the box to sync this phone over Wi-Fi in iTunes, then the syncing has been reliable for me with both an iPhone 5 and iPhone 7 since the last year of iTunes updates (prior to that, it was very problematic).
Surely it can't automatically sync over wifi - it would be stuck in a continual sync...mine have always synced on demand over wifi and automatically when you connect via cable. I haven't noticed any change to that behaviour with 10.13.6 so far...
Or am I misunderstanding the problem?
“When the computer and the iOS device are on the same Wi-Fi network, the iOS device appears in iTunes. The iOS device syncs automatically whenever it charges and iTunes is open on the computer. Learn more about what you can sync and how to sync specific items.” https://support.apple.com/en-us/ht203075
They still sync over WiFi automatically (and on demand as you mention) - if the Mac is awake when I plug the iPad into power. Previously, plugging in the iPad to power would wake the Mac, then sync would start.