I am also having this issue. Just finished adding the Thermaltake Pacific CL360 Max D5 Hard Tube Water Cooling Kit to my system. The reason I chose Thermaltake over Corsair is so that I could sync it with my Razor KB/Mouse/Gamepad. I am having the same issue as the others. Razer Synapse is working with the Asus connect service without issue, it is only ThermalTake that is having this issue.
I am using TT RGB Plus v1.3.7 and Razor Synapse 3.5.831.82315 on Windows 10 version 2004 (OS Build 19041.450).