Stuck on Downloading Messages from iCloud

I Set up iCloud iMessage Syncing on all my devices yesterday; iPhone, iPad, MacBook Pro, and my Mac Pro. All of them synced up except my Mac Pro has been stuck on "Downloading Messages from iCloud" since yesterday (going on 24 hours now). I have quit the application, re-booted my computer, but to no avail. And yes, I updated both my MacBook Pro and my Mac Pro to the latest 10.13.5, as well as my iPhone and iPad to iOS 11.4. My iCloud account is properly set up on all my devices. I have a great internet connection (1 Gig) and no firewall issues. My MacBook Pro is on the same network as my Mac Pro and it updated perfectly and quickly.

Anyone else having this problem? I saw the same issue addressed on MacRumors.com but no solution yet.