I was able to connect using a USB cable, but could not via WiFi, despite being on the same network.
The problem was the firewall. I typed "firewall' into the start button, hit return. 'Help protect your PC with Windows Firewall' dialog appeared. Clicked the 'Allow an app or feature through Windows Firewall' link on the left side, at the top. Scrolled down the list and found SideSync 4.0, sure enough it was not checked. Initially could not check the box to enable, very strange. You need to first click the Change Settings shielded button above the list, then you can check and enable SideSync 4.0, I turned on both Private and Public.
Restarted SideSync and it almost immediately found the phone.
Always so frustrating when a company does such an excellent job on a product, but only takes it to 99%. The installer should have automatically made the exception in the firewall. They could at least interview 50 people using SideSync for the first time, every one of them would have this issue. Very few products I use have I ever needed to make special firewall accommodations for them. If anything the software install should have at least suggested to make a firewall exception. Instead I spent two days on two different computers digging around on support sites to find out it was something stupid like the firewall. Like handing out cans of soup to people at a picnic, and no one brought a can opener, sort of defeats the purpose, no matter how good or tasty your product is.