Form validation loses error bags and old input values on redirect

Hi there !

I have a view which contains a form

@extends('layouts.structure')

@section('content')
@if ($errors->any())
    <div class="alert alert-danger">
        <ul>
            @foreach ($errors->all() as $error)
                <li>{{ $error }}</li>
            @endforeach
        </ul>
    </div>
@endif

<form class="row" action="{{ route('lists.rules.create.store', ['list' => $list, 'condition' => $condition]) }}" method="POST">
    @csrf
    <!-- some form fields -->
</form> 
@endsection

And for the form, I have a controller, defined like so :

<?php

namespace App\Http\Controllers\Lists\Rules;

use App\Http\Controllers\Controller;
use App\Models\ListUser;
use App\Models\ListUserRule;
use App\Models\ListUserRuleFlag;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Redirect;
use Illuminate\Support\Facades\Validator as ValidatorFacade;
use Illuminate\Validation\Validator;

class StoreListUserRuleController extends Controller
{
    private ListUser $list;

    private function handleCreateCollectivities(): ListUserRule|Validator|null
    {
        $request = request();
        $validator = ValidatorFacade::make($request->all(), [
            'level' => 'required|exists:App\Models\Level,id',
            'collectivities' => 'required|array|min:1',
            'collectivities.*' => 'exists:App\Models\Collectivity,id',
            'children' => 'required',
            'neighboors' => 'required',
        ]);

        if ($validator->fails()) {
            return $validator;
        }

        $rule = ListUserRule::create();
        $this->list->rules()->save($rule);
        $rule->collectivities()->saveMany($request->input('collectivities'));
        $rule->flags()->saveMany([
            new ListUserRuleFlag(['name' => 'children', 'value' => $request->input('children')]),
            new ListUserRuleFlag(['name' => 'neighboors', 'value' => $request->input('neighboors')])
        ]);

        return $rule;
    }

    public function __invoke(Request $request, ListUser $list, string $condition)
    {
        $this->list = $list;

        switch ($condition) {
            case 'collectivites':
                $ret = $this->handleCreateCollectivities();
                if ($ret instanceof Validator) {
                    return Redirect::back()->withErrors($ret)->withInput();
                }
                return redirect()->route('lists.show', ['list' => $list]);
            case 'mandats':
                break;
            case 'etiquettes':
                break;
            case 'nuances':
                break;
            case 'champs':
                break;
        }
    }
}

However, upon form submission, when I have errors the error bag is empty and so is the old input one.

I have noticed in the Laravel Debugbar that 2 requests are actually being made : the form's POST (the response of which contains the error bags etc) followed by a GET to the route where the form is.

This SO post (questions ID is 38058223, sorry can't link it on my first day !) showcases the exact same behavior, however I cannot rely on removing the web middleware (which didn't work anyways).

Do you guys have any idea of what the issue might be and how to solve it ?

Thank you in advance for your help ! Yours