Subject: bug#35472:

From: Leo Famulari <[email-masked]>
Date: Mon, 9 Aug 2021 14:56:17 -0400

On Mon, Aug 09, 2021 at 01:54:15PM -0400, François-René Rideau wrote:
>             (nix (file-system
>                   (device "/nixos/nix")
>                   (mount-point "/nix")
>                   ;;(type "bind") ;; fails both at CLI and during reconfigure
>                   (type "none") (option "bind") ;; CLI OK, reconfigure FAIL
>                   (dependencies (list nixos)))))

Try replacing the option field with (flags '(bind-mount))

https://guix.gnu.org/manual/en/html_node/File-Systems.html