Can you open up the “Web Developer Tools” dialog and check what’s reported under the “Network” tab? The shortcut for the Developer Tool is usually Ctrl+Shift+I. You can access it from the browser menus too.
Navigate to the router System Settings page, then open the Developer Tools dialog. Switch to the Developer Tools Network tab.
Click on the “Check for Update” button on the System Settings page, then click on “Upgrade”. There will be a bunch of “sync_time” GET requests and two POST requests. Please send screenshots of the responses to the two POST requests to [email protected].
Switch to the Developer Tools Console tab. Do you see any errors reported there?