To resolve this issue, please try the following options:
Change the URL to include the Fully Qualified Domain Name
Check the URL of your login page, the domain portion of the address should be in the format of a Fully Qualified Domain Name (FQDN). For example, in the URL https://on-premise.avast.com/login/#login "on-premise.avast.com" is the FQDN. Whereas, https://on-premise/login/#login does not contain an FQDN.
To identify the FQDN of a computer you can open the command prompt and enter the command "ipconfig", the FQDN for a device is the non FQDN (such as "on-premise" as shown in the example above) followed by a period and then the Connect-specific DNS Suffix shown when you run "ipconfig". In the example shown, the Connection-specific DNS Suffix would be "avast.com", therefore the FQDN of the device running the On-Premise console would be "on-premise.avast.com"
Use the Server's Static IP Address
In some cases, an FQDN may not be the best options, such as in environments where not all DNS servers are able to resolve the Connection-specific DNS Suffix that your console is using. If this is the case, or if the solution above does not work you may instead choose to ensure that your Console's server has a Static IP or DHCP reservation, then replace the domain in your console's URL with the Server's IP Address.
User a Different Browser
The cause of this issue is isolated to Internet Explorer and Edge browsers. If you have another browser such as Google Chrome or Mozilla Firefox you should be able to access your console without any difficulties.
If You are Unable to Register Installed Devices
After successfully logging in to your console and installing the Antivirus on several devices it is also possible that devices may not appear in your console. If this occurs it indicates that the hostname selected during installation either was not an FQDN, or that the DNS for those devices is not able to resolve the hostname chosen. If this occurs you will need to uninstall your On-Premise Console, then reinstall and select an FQDN hostname that all devices are able to resolve, or use the On-Premise Console server's static IP address as the hostname.