This is a more up-to-date log where a problem in my environment (both on
local and build host) was fixed:

mdj@hat:~$ guix offload test
guix offload: testing 1 build machines defined in
'/etc/guix/machines.scm'...
guix offload: Guix is usable on 'wand.pdc.kth.se' (test returned
"/gnu/store/883yjkl46dxw9mzykykmbs0yzwyxm17z-test")
guix offload: 'wand.pdc.kth.se' is running GNU Guile 3.0.1
sending 1 store item (0 MiB) to 'wand.pdc.kth.se'...
exporting path `/gnu/store/gl7dps3yx0vrxz16sj7q3w7gs3vdbxj4-export-test'
;;; [2020/03/18 20:53:04.930901, 0] write_to_channel_port: [GSSH ERROR]
Remote channel is closed: #<input-output: channel (open) 7f5ed680e780>
Backtrace:
           1 (primitive-load "/home/mdj/.config/guix/current/bin/guix")
In guix/ui.scm:
  1833:12  0 (run-guix-command _ . _)

guix/ui.scm:1833:12: In procedure run-guix-command:
Throw to key `guile-ssh-error' with args `("write_to_channel_port" "Remote
channel is closed" #<input-output: channel (open) 7f5ed680e780> #f)'.