Recently, many people on the #guix IRC channel reported frequent non-deterministic failures of any operation involving substitution, like this:
------ $ ./pre-inst-env guix build --no-grafts poezio mpdris2 sonata beets-bandcamp beets substitute: guix build: error: got unexpected path `Backtrace:' from substituter ------ `guix describe` reports commit b4384e61165623b16b77b8cab16c81423c6853ed for both my user's Guix and the guix-dameon.