From the comments to the question, it was found out that session authentication cookies are set without explicitly specifying the domain. As a result, they operate only on the main domain (where they were installed).
For session authentication cookies to be visible on subdomains, you need to explicitly specify your domain in the config / session.php file
/* |-------------------------------------------------------------------------- | Session Cookie Domain |-------------------------------------------------------------------------- | | Here you may change the domain of the cookie used to identify a session | in your application. This will determine which domains the cookie is | available to in your application. A sensible default has been set. | */ 'domain' => env('SESSION_DOMAIN', null),
So
'domain' => 'your.site',
(previously, a starting point was needed in the domain name so that the cookies were visible on the subdomains, now, according to the new rules, this is not required).
path=/;here the domain must be specified so that the cookie is visible in the subdomains too. - Visman