As of yesterday, we can longer resolve any individual package from our private feed in under 50s. This is affecting all installs with YARN and with NPM, neither makes a difference. This is also the case for any packages the MyGet passes through from the NPMJS' registry. This started yesterday, which unfortunately corresponds with GitHub's major 8 hour outage. I've opened support ticket #3839 12+ hours ago without response.
Please let me know what other information I can provide you here that is considered non-sensitive to help us get this resolved.