With a 2011 Mac Mini running MacOS 10.13.4, everything was working fine until I upgraded to Universal Control v2.7 (build 47644). Symptoms as you describe. Uninstalling the drivers, rebooting and reverting to v2.7 (build 47164) and everything works again.
However, I am still having issues with a 2015 MBP. Was previously working flawlessly with 10.13.4, but now does not properly connect to the Quantum 2 after upgrading to 10.13.5 (regardless if using build 47644 or 47164).