Microsoft is not going to release any Windows 10 / Windows 10 Mobile new build to Insiders in Fast Ring this week. Reason behind this is up-gradation of Insider update services by Microsoft. Microsoft has also advised against making any changes to Ring settings as it will be ineffective until the service upgrade has finished. Here is what Microsoft posted in Feedback Hub.

Hello Windows Insiders,
We are performing some upgrades this week to our services that are used to approve and monitor builds from the Development Branch to our Windows Insiders. Once the upgrade is complete, just as we flight the OS through the rings, we will be flighting the service upgrades through the internal rings first. We won’t have any new builds from the Development Branch for you this week, but plan to return to schedule next week.

As part of this upgrade, any changes to the Windows Insider ring settings via Settings > Update & Security > Windows Insider Program will not take effect until the service upgrade has finished. If you are setting up a new device or changing rings, your device will not receive new builds available to that ring until the upgrade is complete.
In the meantime, keep sending us feedback on any issues you run into on the latest Insider Preview builds via Feedback Hub.