Did you expect that Windows 10 build will soon be updated to Lumia 520 and 525 and yes the 526 variant too? Then you should be informed that there is a delay and you will roll back to 8.1 version. Multiple users report that they bricked their devices doing so with the Windows Phone Recover Tool.Microsoft has therefore delayed the update while the matter is being investigated. The Microsoft team is working to resolve the situation.The users are also reporting similar issues with Lumia 920. They are also offering solutions but it would be best to wait for the official team’s decision.

Microsoft Lumia 520, 525 update delays due to bricking