Can you check that if the issue occure, visit 
http://alm.stef.com:8080/qcbin/rest/is-authenticated
what headers and values would you get in the response?

the error occured yesterday:

• http://alm.stef.com:8080/qcbin/rest/is-authenticated

  Error 401 Authentication failed. Browser based integrations - to login append '?login-form-required=y' to the url you tried to access.
  h2. HTTP ERROR 401
  
  Problem accessing /qcbin/rest/is-authenticated. Reason:
  
  Authentication failed. Browser based integrations - to login append '?login-form-required=y' to the url you tried to access.
  
   
  ----
  Powered by Jetty://
   

Headers:

Cache-Control →must-revalidate,no-cache,no-store
Content-Length →541
Content-Type →text/html; charset=ISO-8859-1
Date →Wed, 28 Jun 2017 08:13:03 GMT
Server →Jetty(9.1.4.v20140401)
WWW-Authenticate →LWSSO realm="http://alm.stef.com:8080/qcbin/authentication-point"

Hi Raphaël UNIQUE,

The response seems ok. I suggest you to submit a ALM case, a private channel. Because this problem need further investigation.  Something may not proper to communicate here in a public place.

Since it not always happens. I guess it's because of network problem or ALM down.

Salut Raphaël, 

I think the problem come from the version of parametrized-remote-trigger-plugin plugin, the value of cookie is setting statically.

Check you  parametrized-remote-trigger-plugin version, it should not be (3.0.0 ~ 3.0.4)

Hi Tarik,

version deployed: 3.0.6