The extensions in your list (except the first one) are al templates, so they should not be availble in the client, but can be used in the dev-hub as templates for new extensions (or mashups).
For the first one, admin-test:
- verify that the qext file is valid JSON
- check type "type" property in the qext file, it should be "visualization"
You coul also check for errors in the browser console.