Since we wanted to allow the law firm to continue to operate durring the switch over we setup new phone lines at the new telco, then wired in the new system along side the old system so at one point each employee had two phones at their desk.
This has been an ongoing issue for some time for a number of my clients. (Since about August 2016) Google Drive would not load in Chrome and sometimes Firefox and Safari unless in Incognito Mode. When I consulted Google about it they asked me to create a symbolic link from the home folder ~/Library/Application Data to the local drive. This only solved it for the user I did it for, it was not a universal solution. The following is a universal solution but its less than ideal.