This is a high priority for us to solve and have a team dedicated to it. We will let you know as soon as we have info on recovery.
— Gabriel Aul (@GabeAul) September 17, 2015
Microsoft earlier this week released Windows 10 Mobile build 10536 to Fast Ring Windows Insider program users. This build is supported in most of the Lumia devices, but there are several other Windows Phone devices which are not supported with Windows 10 Mobile builds. There was a bug which allowed several non-supported devices to install this latest build from Microsoft and Microsoft issued warning to users to not install it. Since the update was offered to them, several HTC 8X, BLU and some other Windows Phone users installed it. Microsoft is now working to find repair options to recover these devices. They have a team dedicated to it and working on high priority.