Microsoft has accidentally released Windows 10 Mobile Build 16212 to Windows Insiders in the Fast, Slow and Release Preview Ring. If you’ve installed Windows 10 Mobile Build 16212 on your Windows Phone, your phone will be stuck in a reboot loop.
Microsoft has released the same buggy build to Windows 10 PCs, however the solution for PCs and tablets is easy. But on Windows 10 Mobile you will need to recover your phone by wiping the entire data stored on the device.
How to recover a bricked Windows 10 Mobile
Microsoft has detailed as to how you can recover your bricked Windows 10 Mobile device that is stuck in a reboot loop. The only way to recover your Windows Phone is to use the Windows Device Recovery Tool and re-flash the device. After re-flashing your Windows Phone. You will need to restore the backup and again join the Windows Insider Program on your device.
How to stop Windows 10 Mobile from installing builds and updates
In case, your phone has downloaded the build but has not installed the build. You will need to reset your phone and you can do that by navigating to Settings > System > About – Reset.
Microsoft’s Dona Sarkar explained the issue, “This happened because an inadvertent deployment to the engineering system that controls which builds/which rings to push out to insiders,” (Source: Blogs.Windows.com).