Slug add number instead of a string

[Leeuwenkasteel]

I used your packages in a few projects, it alsway work perfect. But nog he add a number instead of a string

<?php

namespace Leeuwenkasteel\Menu\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;
use Carbon\Carbon;
use Spatie\Sluggable\HasSlug;
use Spatie\Sluggable\SlugOptions;

class Menu extends Model
{
    use HasFactory;
    use HasSlug;

    protected $table    = "menu";
    protected $fillable = ['title', 'slug', 'folder_id', 'icon', 'active'];
    protected $dates    = ['deleted_at','created_at', 'updated_at'];

    public function getSlugOptions() : SlugOptions
    {
        return SlugOptions::create()
            ->generateSlugsFrom('title')
            ->saveSlugsTo('slug');
    }