Te dejo este enlace
https://www.3cx.com/blog/releases/upgrade-debian-10-buster/
La actualización va a fallar cuando esa instalación haya sufrido una de las siguientes condiciones:
Manually added repositories.
Manually installed packages, causing dependencies issues.
Changed or removed default Debian repositories.
Remote administration tools such as Ansible and Puppet that could interfere during the upgrade process (e.g locking APT during the process).
Altered locale or TZdata without updating the OS fully via dpkg commands.
Modified/broken nginx configuration files.
Tampered root certificates.
Restricted internet access for apt to call the update (outbound port 80 is required).
Por lo que les sugiero tomen un backup, desinstalen e instalen una nueva máquina fresca con el último archivo ISO.
Un saludo!
