The problem was that the client distributed with server 2.2.7 would replace the custom settings, including the Internet server IP address and key, with the default settings which were empty. On a local network the client could easily find the server and all was well, but an Internet client has no clue where to look.
Once the server is upgraded to 2.2.8 you need to download a fresh copy of the configured Internet backup client from the server for each Internet client, using the buttons at the bottom of the status screen. Uninstall the current UrBackup client program from each Internet client computer to delete the bad settings, and install the fresh client program in its place. If you try to install a new client over an existing one, the installer will leave the current settings files alone and use them with the new program.
Once this custom client software is installed on each client computer, the settings will be correct and it will talk to the server again. Previous backups are still in place and incremental backups will resume properly.
If you had custom settings for the files or directories to back up for this client you will need to configure that before you begin backups. I prefer to make all such changes at the server. In the Clients box select the client to be configured. Mark “Separate settings for this client”, and under Permissions, clear “Allow client-side changing of the directories to backup” and “Allow client-side changing of settings”. This way the correct settings will be copied to the client before a backup.