We noticed similar behavior reported by our monitoring as well. We still not sure we understand the root cause but believe that it is related to the Hyper-V networking issues on some hosts. We are rolling out the fix which we hope should help. Infrastructure level changes are not very fast to deploy, so it will be fully deployed in 24-48 hours. Please send us a links to the failed builds if you hit it again.
I'm a colleague of Boris and am running into similar issues. I realize 24-48 hours have not yet passed, but only about 12 hours so far. At the moment we're still experiencing the issues, e.g. this build just now: