user_id in Session always null - Custom User Provider

Hi dear community,

currently I am building a site with two user tables.

I am using the default users table for my backend users and the rm_users for logging in users from another remote server.

I added this user provider to my auth.php

'msr_users' => [
    'driver' => 'eloquent',
    'model' => \Modules\Frontend\Models\UserMsr::class,
 ],

and I also added this to the guards array

 'web_msr' => [
    'driver' => 'session',
    'provider' => 'msr_users',
 ]

also I have added a custom password reset for the rm_users

'msr_users' => [
    'provider'  => 'msr_users',
    'table'     => 'rm_users_password_resets',
    'expire'    => 60,
]

additionally this middlewares are defined

 'msr_user_auth' => \Modules\Frontend\Http\Middleware\AuthenticateMsrUser::class,
 'msr_user_guest' => \Modules\Frontend\Http\Middleware\RedirectIfMsrUserAuthenticated::class

<?php

namespace Modules\Frontend\Http\Middleware;

use Closure;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Auth;

class RedirectIfMsrUserAuthenticated
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle(Request $request, Closure $next)
    {
        if (Auth::guard()->check()) {
            return redirect('/');
        }

        if (Auth::guard('web_msr')->check()) {
            return redirect('/profil');
        }

        return $next($request);
    }
}

<?php

namespace Modules\Frontend\Http\Middleware;

use Closure;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Auth;

class AuthenticateMsrUser
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle(Request $request, Closure $next)
    {
        if (! Auth::guard('web_msr')->check()) {
            return redirect('/anmelden');
        }

        return $next($request);
    }
}

Of course I have separate Controllers for both logins (rm_users and users). The necessary overrides are made within those controllers.

Everything works fine so far, I can log in by checking the username in the rm_users table. Also the session is created, but I noticed that the user_id within the sessions table always stays null.

As soon as I login as a backend user from the default users table it just works fine (I have separate login routes for remote and default backend users).

Am I missing something in here? I haven't created a dedicated guard or user provider class, as I am using the default mechanism, I am not sure if this is the problem?

Does it make sense to have a separate custom session tables for the remote users? I don't know if this is even easily possible within laravel.

I hope you can guide me into the right direction.

Best Regards.