Updated June 2, 2017: Windows Insider Program head, Dona Sarkar, has acknowledged the unintentional rollout of internal builds to both PC and Mobile. Since yesterday's fiasco both builds are no longer being offered, with no new builds planned for the rest of this week. While PC users have the option to roll back to a previous build, those who installed the rogue build on Mobile can restore their device via WDRT.

Microsoft is having some major issues with its Windows Insider Program right now, on all rings affecting many different device types. If you're a Windows 10 Mobile user, do not install build 16212 being offered to you, as this will cause your phone to enter a boot loop, requiring you to reset your phone with the Windows Device Recovery Tool.

Some PCs are also receiving bad builds, on all the Insider Rings. If you're seeing build 16212 from the rs_edge_case branch, do not install this build either. Microsoft appears to be suffering from an internal issue that is causing several development builds of Windows 10 to rollout publicly to Insiders.

We suggest you leave the Insider Program for the time being, until Microsoft fixes the issue and stops these rogue builds from rolling out to the public.