My Visual Studio started taking a longish- three to four minutes to load up and then the same when I opened a project. This started after the last Xamarin update. I’ve always found that for best results I have to reboot after an update and then unpair and pair. Sometimes my Mac Mini shows up in the Connection dialog as an IP address and sometime as the name. As the ip is DHCP provided, I figured out using the name was best however..
To cut a long story short, Zone Alarm did not like DNS queries for the Virgin DNS ( 18.104.22.168 and 22.214.171.124 port 53 ) which were resolving the Mac Mini and it was those being blocked that slowed VS down. I figure it must have been a timeout plus maybe some kind of fallback as I could still build projects on the Mac.
So if you ever get that kind of slow down, check your firewall!