Make sure your Application Links are created correctly in both your Jira and Confluence instances:
Confluence:
Jira:
Make sure your external gadgets are provisioned in the Confluence administration, one by one or registered as a feed to subscribe to all gadgets from your Jira instance:
Try referencing a gadget directly in the Confluence page by using its XML URL and see if it works:
Example:
{gadget:url=http://localhost:8080/rest/gadgets/1.0/g/com.xpandit.plugins.xray:overall-test-results-gadget/gadgets/overall-test-results-gadget/overall-test-results-gadget.xml|width=800}
{gadget:url=http://localhost:8080/rest/gadgets/1.0/g/com.xpandit.plugins.xray:test-runs-summary-gadget/gadgets/test-runs-summary-gadget/test-runs-summary-gadget.xml|width=1200}
