Symfony profiler throws 404

It's often problem with event subscriber/listener.Try run

console debug:event

And check for errors

This usually happens if the cache directory is not properly set up to allow the web servers' user to write data into them.

Under Linux, I would usually use this for development:

php app/console --env=dev cache:clearphp app/console --env=dev cache:warmupchmod -R a+rwX app/cache/setfacl -Rm g:www-data:rwX app/cache/setfacl -Rm g:dev-user:rwX app/cache/

This ensures all required directories will be created and then assigned the required permissions. If you do not have ACL enabled, skip the setfacl commands.

OFC, replace www-data with your web servers' username, and dev-user with your username.

This is a known bug in the profiler. Since Symfony 2.4, the profiler persisting the data used by the WDT is the very last thing done by Symfony.

The alert you see means that the profiler has not been able to find the token requested in the 2500ms allowed, However if you click OK in the alert, you should be redirected to the profiler and figure out what precisely is slow.