Follow the instructions below:
Log on to the machine where you want to run multiple instances of Veeam ONE Monitor Client.
Open registry editor and navigate to the following registry key:
for v5.0 - HKEY_CURRENT_USER\Software\Veeam\Veeam Monitor for VMware
for v6.0 and higher - HKEY_CURRENT_USER\Software\Veeam\Veeam ONE Monitor
Create a new value with the following settings:
Type - DWORD
Name - AllowMultMonitors
Value data - 1
As a result, you will be able to run multiple instances of Veeam ONE Monitor Client on a single machine.