I tried a
nix-channel --update dhall and I got an error which ultimately seems to be because https://hydra.dhall-lang.org/jobset/dhall-haskell/master/channel/latest is throwing a 500.
I’m not sure how to report problems with hydra other than on here.
By the way, I’d be happy to help with administering these resources if someone wants to grant me access. I am a developer/sysadmin in my day job and I run NixOS on my personal machine, and though I haven’t got direct experience of running hydra I’m sure I could work it out