We're getting an issue with all our clients at a major corporation with offices around the globe.
Any Mac at this client we upgraded from v6.x.x to 19 (including the latest 19.5) keep dropping off the network and won't refresh or allow a connection
The temporary cure is remove all of the current version and reinstall 6.0, which is very tricky when you can't connect to them remotely.
We've also taken a client machine running 19.5 that works fine in our offices in Oxford down to the companies UK office and it stops connecting on their network.
Customer support service by UserEcho