Is this something related with? 

• https://webmasters.stackexchange.com/a/128680
• https://www.chromium.org/updates/same-site/faq

You are saying your session is 'destroyed'. I think you should investigate if this is truly the case. You need to confirm if your session cookie is still available. If so, could there be a reason that the session is 'removed'? Sessions (and also the session cookie) have a limited lifetime. 

There might also be another reason that the session is 'reset'. You can check that by looking at the identifier in the session cookie. If that changes, something reset the session. This normally only happens when a user logs in/out.

Be aware that session data is not copied from a logged out user to a logged in user. So if you have done something in your session as a logged out user and that user logs in, he/she loses the session data (as a new session is generated on login). If you need logged out user session data transferred to the logged in user, you need to copy this somewhere in your code.

Hi Nikolai Shcherbin,
Thank you for your answer... but for example via a link with no Latin character i have the same problem: https://www.silencecommunity.com/file/view/428/modifiez-votre-profil no "downloading function".

I see this now.

The timestamps of files has changed after a migration to a new server.

Try this:

• Disable all caching settings on your site via /admin/settings/advanced
• As Elgg docs suggested:

You also need to delete the views cache on the test server after the copy process. This is a directory called views_simplecache in your data directory and the directory called system_cache .

• Run 'Flush the caches' via Administration
• Check your problem URLs again.
• Enable the caching on the site.

Read this also.

Thank you very much Nikolai Shcherbin ater this SQL query it works! Wonderful! :-) Thanks so much for your help.

Change the filestore data directory

UPDATE elgg_metastrings SET string = '/var/data/elgg_test/'
WHERE id = (
   SELECT value_id
   FROM elgg_metadata
   WHERE name_id = (
      SELECT *
      FROM (
         SELECT id
         FROM elgg_metastrings
         WHERE string = 'filestore::dir_root'
      ) as ms2
   )
   LIMIT 1
);

I don't fully understand what you are asking for. You posted the same url twice, so I don't know which one you see when. The action/actions matter is something to do with rewrite rules and the difference between urls and filesystem paths. You would use action is urls but the folder is to be named actions. When registering an action correctly, Elgg should deal with action/actions correctly. When registering an action you would also have to define if the action can be called only by users logged in or also be logged-out anonymous visitors (or only by admins). If you have enabled the option to restrict access to pages to logged in users only, it would also happen that trying to access a page not defined as "public page" when not logged in will get you redirected to the login page.

Sorry, I had missed the rule in htaccess i.e. RewriteBase /