A registered user can't declare herself as a user of a software

Steps to reproduce

1. On Comptoir v2.4.9, log in (no matter the kind of user)
2. Go to the a software page (say Asqatasun page)
3. Declare yourself as user of this software
4. You are redirected to an error message: This page does not exist and you are not added a user of the software

Logs

Excerpt of error.log:

2018-08-30 09:45:04 Error: [Cake\Routing\Exception\MissingControllerException] Controller class Softwares could not be found.
Request URL: /softwares/users-software/9
Referer URL: https://www.comptoir-du-libre.org/softwares/9
Client IP: 109.190.216.28
Stack Trace:
#0 /home/comptoir/Comptoir-srv/vendor/cakephp/cakephp/src/Http/ControllerFactory.php(72): Cake\Http\ControllerFactory->missingController(Object(Cake\Network\Request))
#1 /home/comptoir/Comptoir-srv/vendor/cakephp/cakephp/src/Routing/Filter/ControllerFactoryFilter.php(63): Cake\Http\ControllerFactory->create(Object(Cake\Network\Request), Object(Cake\Network\Response))
#2 /home/comptoir/Comptoir-srv/vendor/cakephp/cakephp/src/Routing/Filter/ControllerFactoryFilter.php(49): Cake\Routing\Filter\ControllerFactoryFilter->_getController(Object(Cake\Network\Request), Object(Cake\Network\Response))
#3 /home/comptoir/Comptoir-srv/vendor/cakephp/cakephp/src/Routing/DispatcherFilter.php(144): Cake\Routing\Filter\ControllerFactoryFilter->beforeDispatch(Object(Cake\Event\Event))
#4 /home/comptoir/Comptoir-srv/vendor/cakephp/cakephp/src/Event/EventManager.php(426): Cake\Routing\DispatcherFilter->handle(Object(Cake\Event\Event), Object(Cake\Network\Request), Object(Cake\Network\Response))
#5 /home/comptoir/Comptoir-srv/vendor/cakephp/cakephp/src/Event/EventManager.php(391): Cake\Event\EventManager->_callListener(Array, Object(Cake\Event\Event))
#6 /home/comptoir/Comptoir-srv/vendor/cakephp/cakephp/src/Event/EventDispatcherTrait.php(78): Cake\Event\EventManager->dispatch(Object(Cake\Event\Event))
#7 /home/comptoir/Comptoir-srv/vendor/cakephp/cakephp/src/Http/ActionDispatcher.php(80): Cake\Http\ActionDispatcher->dispatchEvent('Dispatcher.befo...', Array)
#8 /home/comptoir/Comptoir-srv/vendor/cakephp/cakephp/src/Routing/Dispatcher.php(60): Cake\Http\ActionDispatcher->dispatch(Object(Cake\Network\Request), Object(Cake\Network\Response))
#9 /home/comptoir/Comptoir-srv/webroot/index.php(36): Cake\Routing\Dispatcher->dispatch(Object(Cake\Network\Request), Object(Cake\Network\Response))
#10 {main}