This Question is related to my Question Combining “Gated Checkin” and “Continuous Integration” Builds in Team Foundation Server I Posted this Morning
Thanks to @pant
For vNext builds, check the "Run continuous integration triggers for committed changes" option on the Triggers tab for a build.
See the section "Option to run CI builds" in this reference:: https://docs.microsoft.com/en-us/vsts/build-release/concepts/definitions/build/triggers#gated