Are you building in a clean chroot? And can you push your package somewhere? (The pasted logs don't give much clue)
I'm building in a sid container that I've created for packaging. I haven't done much with the package, I just generated the files with gem2deb and imported them to a git repo. I have pushed everything here[1]. [1]: https://salsa.debian.org/abraham/ruby-omniauth-rails-csrf-protection - Abraham
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