Comment 36 for bug 1840232

Since you have so many files in /opt, the issue may be with inodes (https://en.wikipedia.org/wiki/Inode).

Would you please test the the *Development* branch, and let me know if it resolves your problem?

    # Remove Cubic
    $ sudo apt autoremove --purge cubic

    # Remove the *Release* repository
    $ sudo apt-add-repository --remove ppa:cubic-wizard/release

    # Add the *Development* repository
    $ sudo add-apt-repository ppa:cubic-wizard/development

    # Install the *Development* version of Cubic
    $ sudo apt update
    $ sudo apt install cubic

In the Development branch (revision 209), I've changed "cache-inodes" to "-no-cache-inodes" for mkisofs, as an experiment (see https://linux.die.net/man/8/mkisofs).

With "-cache-inodes", hard links (files with multiple names) only appear once on the CD. However, with "-no-cache-inodes", multiple hard links to the same file are repeated.

The drawback is that the resulting image may actually be larger. (For this reason, I'm not sure I would introduce this experimental "fix" as a permanent change to Cubic, but it's worth checking to see if it resolves your particular problem where you have many, many files).