This is a known bug, caused by elpa not keeping history the way we’d like it to: ELPA packages are fetched from unstable url -> not reproducible · Issue #55 · nix-community/emacs2nix · GitHub
It needs some reviving.
The issue that sparked that one points to a workaround: Override a transitive emacs dependency - #4 by codygman
Personally I’ve been using unstable for these packages, since they’re usually not broken for long there and it’s less faff than managing overrides.