Getting a similar failure here:

$ guix import go github.com/cncf/udpa/go/

following redirection to `https://proxy.golang.org/github.com/cncf/udpa/go/@v/list'...
following redirection to `https://proxy.golang.org/github.com/cncf/udpa/go/@latest'...
following redirection to `https://proxy.golang.org/github.com/cncf/udpa/go/@v/v0.0.0-20210322005330-6414d713912e.mod'...
guix import: warning: Failed to import package "github.com/cncf/udpa/go/".
reason: ("vector-ref" "Wrong type argument in position 1 (expecting vector): ~S" (#f) (#f)).
guix import: error: failed to download meta-data for module 'github.com/cncf/udpa/go/'