Initiate iTunes Wi-Fi Sync from iOS device

I recently purchased a 2018 model Mac mini, and have set my iOS devices to back up to this computer with sync over wifi enabled. I performed the initial sync via USB, and have been able to perform subsequent sync activities over wifi when I initiate the sync from iTunes on my Mac. However, my iOS devices still display the following message in Settings > General > iTunes Wi-Fi Sync:

"To enable Wi-Fi syncing with iTunes, connect to iTunes on your computer using a cable and click 'Sync with this [iDevice] over Wi-Fi.'"

I have reconnected each device with a cable, deselected and reselected the wifi sync option, rebooted the devices and Mac, and tried performing the same activities with the Mac booted in Safe Mode (per Apple's suggestion). None of these things have worked, I have yet to be able to see the "Sync Now" option in the Settings for any of my iOS devices. Configuration as follows:

Mac mini 2018, 10.14.2 (iTunes 12.9.2.5)

iPhone 7, 12.1.3

iPad Pro 10.5", 12.1.3

iPhone X, 12.1.3

iPad Air 2, 12.1.3

All devices on same wifi network and subnet, sync over wifi works when initiated from iTunes on Mac.

Any other suggestions are appreciated!