Please use modern UI IE to access the Internet, if there is any issue occur, Windows will run network diagnose automatically.
Meanwhile, please configure the following group policy for a test.
1. Open "Local Group Policy Editor"
2. Navigate to "Computer Configuration - Administrative Templates - Network Isolation"
3. Open "Internet Proxy Servers for Metro Style Apps" and set the value to your proxy server address like 172.16.0.1:8080.
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