fhsUserEnv has stopped working

I am unable to use fhsUserEnvs since the last time I upgraded nixos. Any attempt to use fhsuserenv fails with an error saying “main: unshare: No space left on device”. The error persists even if I boot into the old nixos snapshot. This issue contains more info about the problem: "fhsUserEnv" does not work since last upgrade · Issue #124710 · NixOS/nixpkgs · GitHub . What could be the problem here?

steam still works for me, I think buildFHSUserEnv is just not meant to be ran in this way. Generally the script is launching a process.