Server fails to start with packwiz modpack

[Irgendeinwer]

Hello,
My Fabric server fails to start with any packwiz modpack (repo):

journalctl -eu minecraft-server-cool-modpack.service

Mar 21 18:47:31 lind systemd[1]: Starting Minecraft Server cool-modpack...
Mar 21 18:47:31 lind (ack-stop)[1009]: minecraft-server-cool-modpack.service: Referenced but unset environment variable evaluates to an empty string: MAINPID
Mar 21 18:47:31 lind minecraft-server-cool-modpack-stop[1017]: no server running on /run/minecraft/cool-modpack.sock
Mar 21 18:47:31 lind systemd[1]: minecraft-server-cool-modpack.service: Deactivated successfully.
Mar 21 18:47:32 lind systemd[1]: Started Minecraft Server cool-modpack.
Mar 21 18:47:32 lind systemd[1]: minecraft-server-cool-modpack.service: Consumed 345ms CPU time, 31M memory peak, 25.1M read from disk, 32K written to disk.
Mar 21 18:47:32 lind systemd[1]: minecraft-server-cool-modpack.service: Scheduled restart job, restart counter is at 1.
Mar 21 18:47:32 lind systemd[1]: Starting Minecraft Server cool-modpack...
Mar 21 18:47:32 lind (ack-stop)[1080]: minecraft-server-cool-modpack.service: Referenced but unset environment variable evaluates to an empty string: MAINPID
Mar 21 18:47:32 lind minecraft-server-cool-modpack-stop[1083]: no server running on /run/minecraft/cool-modpack.sock
Mar 21 18:47:32 lind systemd[1]: minecraft-server-cool-modpack.service: Deactivated successfully.
Mar 21 18:47:32 lind systemd[1]: Started Minecraft Server cool-modpack.
Mar 21 18:47:32 lind systemd[1]: minecraft-server-cool-modpack.service: Scheduled restart job, restart counter is at 2.
Mar 21 18:47:32 lind systemd[1]: Starting Minecraft Server cool-modpack...
Mar 21 18:47:33 lind (ack-stop)[1202]: minecraft-server-cool-modpack.service: Referenced but unset environment variable evaluates to an empty string: MAINPID
Mar 21 18:47:33 lind minecraft-server-cool-modpack-stop[1219]: no server running on /run/minecraft/cool-modpack.sock
Mar 21 18:47:33 lind systemd[1]: minecraft-server-cool-modpack.service: Deactivated successfully.
Mar 21 18:47:33 lind systemd[1]: Started Minecraft Server cool-modpack.
Mar 21 18:47:33 lind systemd[1]: minecraft-server-cool-modpack.service: Scheduled restart job, restart counter is at 3.
Mar 21 18:47:33 lind systemd[1]: Starting Minecraft Server cool-modpack...
Mar 21 18:47:33 lind (ack-stop)[1417]: minecraft-server-cool-modpack.service: Referenced but unset environment variable evaluates to an empty string: MAINPID
Mar 21 18:47:33 lind minecraft-server-cool-modpack-stop[1420]: no server running on /run/minecraft/cool-modpack.sock
Mar 21 18:47:33 lind systemd[1]: minecraft-server-cool-modpack.service: Deactivated successfully.
Mar 21 18:47:33 lind systemd[1]: Started Minecraft Server cool-modpack.
Mar 21 18:47:34 lind systemd[1]: minecraft-server-cool-modpack.service: Scheduled restart job, restart counter is at 4.
Mar 21 18:47:34 lind systemd[1]: Starting Minecraft Server cool-modpack...
Mar 21 18:47:34 lind (ack-stop)[1464]: minecraft-server-cool-modpack.service: Referenced but unset environment variable evaluates to an empty string: MAINPID
Mar 21 18:47:34 lind minecraft-server-cool-modpack-stop[1466]: no server running on /run/minecraft/cool-modpack.sock
Mar 21 18:47:34 lind systemd[1]: minecraft-server-cool-modpack.service: Deactivated successfully.
Mar 21 18:47:34 lind systemd[1]: Started Minecraft Server cool-modpack.
Mar 21 18:47:34 lind systemd[1]: minecraft-server-cool-modpack.service: Scheduled restart job, restart counter is at 5.
Mar 21 18:47:34 lind systemd[1]: minecraft-server-cool-modpack.service: Start request repeated too quickly.
Mar 21 18:47:34 lind systemd[1]: minecraft-server-cool-modpack.service: Failed with result 'start-limit-hit'.
Mar 21 18:47:34 lind systemd[1]: Failed to start Minecraft Server cool-modpack.

Things I've tried

• using the modpack with packwiz modrinth export + importing it into Prism Launcher → works fine.
• running a Fabric server with no mods → functions as expected.
• running a Fabric server with a packwiz modpack that contains only a single mod → fails

My nix-minecraft config

{ pkgs, lib, ... }:
let
  modpack = pkgs.fetchPackwizModpack {
    url = "https://codeberg.org/Irgendeinwer/fabric-packwiz/raw/tag/v1.3/pack.toml";
    packHash = "sha256-Hv1CsvokqrzrlHEJTNXyZj1o1dFGl0y0+NTUgqTh/ks=";
    manifestHash = "0bypfaf34bd95x4rh8hlb5ybps5m1g999kqw3bvwgfsvpxplrqs3"; 
  };
  mcVersion = modpack.manifest.versions.minecraft;
  fabricVersion = modpack.manifest.versions.fabric;
  serverVersion = lib.replaceStrings [ "." ] [ "_" ] "fabric-${mcVersion}";
in
{
  services.minecraft-servers = {
    enable = true;
    eula = true;
    openFirewall = true;
    dataDir = "/var/minecraft";
    
    servers.cool-modpack = {
        enable = true;
        autoStart = true;
        whitelist = { # You can use mcuuid.net
            Name = "UUID :O ";
        };
        serverProperties = {
            white-list = true;
            motd = "Fabric on NixOS, btw";
            max-players = 10;
            spawn-protection = 0;
            difficulty = 3;
        };
        jvmOpts = "-Xms6G -Xmx3G";
        package = pkgs.fabricServers.${serverVersion}.override { loaderVersion = fabricVersion; };
        symlinks = {
            "mods" = "${modpack}/mods";
        };
    };
  };
  nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
    "minecraft-server"
  ];
}

Thanks for any answers :)
(And sorry if it was an obvious mistake)

[Irgendeinwer]

Changing jvmOpts = "-Xms6G -Xmx3G"; to jvmOpts = "-Xms6G -Xmx6G"; fixed the problem btw

[Infinidoge]

Ah, yep, that would do it!