I use the softphone desktop app and I see this when I switch workstations.
For me, the reason it happens is because I have not logged into the Admin portal and deauthorized the previous workstation before attempting to login on the current workstation.
There has to be a reason for this, likely security, but it's frustrating having to do all of this daily, some times more than once:
Rincentral.com Load the login page
click on Sign in to bring up the profile login window
Choose my profile
Let the account page load
THEN phones & numbers
THEN 'Deauthorize this computer"
I'd like to see a simple "would you like to deauthorize (whatever) computer" as an option when signing into a new workstation. But I'm probably in the minority as I work in an environment where we do not have assigned seats, so....