Laravel and Passport, random 401 errors

I'm writing a single page web application. I'm using Vue.js in the frontend and Laravel in the backend.

I included Passport token authentication and I'm getting the auth token sending

var login_data = {
            client_id : 2,
            client_secret : "SECRET_KEY",
            grant_type : "password",
            username : "mail,
            password : "pass"
          }

To this Passport endpoint http://IPADDRESS/oauth/token. Then I authenticate my ajax requests including this header

{'Authorization':'Bearer ' + ACC_TOKEN}

Most of the time everything works fine but sometimes I get 401 unauthorized. Usually, if I simply do it again the request goes through.

I removed the VerifyCsrfToken middleware from Kernel.php and also added the API route to the exceptions so I don't think that's the problem.

The frequency the error appears seems to change from network to network, meaning when connected to certain networks it almost never happens while sometimes it's constant.

I honestly have no idea why this happens. Thanks.

via Lorenzo Norcini