Why aren't my local tasks shown? I have the module.routing.yml as 

entity.node.ssl_check:  
  path: '/node/{node}/check-ssl'  
  defaults:  
  _form: '\Drupal\ssl_check\Form\SslCheck'  
  _title: 'Check SSL Cert'  
  requirements:  
  _permission: 'access check ssl tab'  


and module.links.task.yml as 

 entity.node.ssl_check:  
  route_name: entity.node.ssl_check  
  title: 'Ssl check'  
  base_route: entity.node.canonical  
  weight: 15  


Here when I access node/1104/check-ssl/ the form defined in the form controller is loading. But my other need that is to show a 'Ssl check' tab when I visit path /node/1104/ is not there. I have done the tab thing while dealing with Controller but not working with form controller. Please help. I have checked 'Add tab / local task to a node' this but there was nothing dealing with form controller.
Since everything looked just fine in your code, I tried the following in a custom module: 

#test.links.task.yml
test.node_test:
   title: 'Wooorking'
   route_name: entity.node.canonical
   base_route: entity.node.canonical


And this is working like a charm. Also when I added a custom routing, which was pointing to a form controller, it showed up! (although not worked, because I didn't handled the node parameter in the routing configuration)

So the problem lies another where. 

So I suggest you to do it step by step way (building your routing and task yml) to understand your problem. Clearing the cache each time when you change something in your YML files. If you found the problem, please post the solution, so also we can learn from this.