I can't reproduce this problem anymore using this Guix: $ guix describe Generation 59 Feb 28 2020 19:53:52 (current) guix 079ee3b repository URL: https://git.savannah.gnu.org/git/guix.git branch: master commit: 079ee3b5ea7e9e9bf34753df42957d280e8eabc5
I can record the desktop normally again. I couldn't find any specific commit in Guix's git log mentioning this issue, so I don't know when it was fixed. It fixed itself magically.
