Hi there!
dhall-lsp-server has had some configuration defined to use an older version of lsp and newer version bounds on nixpkgs to keep things working. The latest Stackage/Hackage bump breaks things for that pinned version of lsp: NixOS/nixpkgs#279413
I'm assuming dhall-lsp-server as it appears on main branch will work just fine, could we have a new version released to Hackage?