Removing Mullvad causes connection issues in NekoBox

I used to use Mullvad for proxying my Internet connections, but lately switched to other protocols using NekoBox. Since I wasn’t using Mullvad anymore, I decided to remove it from my system configuration, but it lead to issues when using NekoBox in TUN mode. Specifically, all Internet connections start to fail after rebuilding the system and restarting NekoBox. This is how it looks like in the log:


Changing DNS settings in NekoBox doesn’t improve the situation.
nix-info: system: "x86_64-linux", multi-user?: yes, version: nix-env (Nix) 2.18.8, channels(root): "nixos-24.05, nixos-24.05-24.05, unstable", nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos