After the release date of Windows 10 for phones build 10051 (12534), many users get in trouble with the new OS build. Let’s see what they said and how the feedback from Microsoft engineers can solve these problems.

Here is the issue list we know until now:
– Lumia phone does not detect the SIM card
– Getting the update error 80073cf6 when updating the Device Hub
– Lumia gets blocked after entering simcard code
– Cannot open the Setting (mainly on Lumia 520)
– Notification bar can’t be pulled up, blue dot on the upper left corner (mainly on Lumia 535 Dual Sim)
– The device can not sleep
– SIM PIN is locked after upgrade to Windows 10 for phones build 10051

(This list is continuing updated. You can help us via the comment section below or the “GIVE US YOUR FEEDBACK” form in the right hand side.)

Windows 10 for phones issues fixed! See how
Windows 10 for phones issues fixed! See how

Feedback from Microsoft:

Lumia phone does not detect the SIM card after upgrade to Windows 10 Technical Preview phone build 10.0.12534.56
In this case, there is no way that you can do except rolling back to the previous version. How to do that? Just download the Windows Phone Recovery Tool and re-flash your device to Windows Phone 8.1. Before doing so, please ensure you have backed up any important content such as your photos, videos, contacts, etc.
Getting the update error 80073cf6 when updating the Device Hub on Windows 10 Phone 12534.56
Please follow the instruction below:
Set the time and date on your phone manually.  Go to Settings > time + date > turn set automatically OFF > set the time, date and time zone manually.  Once this is done, go to Settings > emails + accounts > tap and hold the Microsoft account > sync.  Once the sync completes, try updating or downloading again.

If the issue still persists, then Please try restarting the phone and check if that helps fix the issue. Else, try resetting it.
Important: Take a backup of all important data.

If the issue still persists, then I would suggest you to provide the feedback via the “GIVE US YOUR FEEDBACK” form in the right hand side so that it will be implemented in future Builds.

Windows Feedback app comes preinstalled in Windows 10 Technical Preview for phones. You can provide the feedback in the feedback app. Click the plus sign(+)  to enter new feedback or click  to sort.  
Lumia gets blocked after entering simcard code
There are 3 ways which could resolve the SIM PIN issue
1. Disable SIM PIN in Settings -> System -> Phone
Or Change SIM in this menu
Settings App Crashes for many people after pressing phone
– Power off your device
– Remove SIM
– Power On
– Open Settings -> System -> Phone
– Power Off
– Insert SIM
– Power On
– Cancel SIM PIN
– Go to Settings -> System -> Phone
– Change or Disable SIM PIN
Your fine to go
Note: If you only change your PIN you never can enter SIM PIN on Startup, you have always change it in Settings! Entering at Phone Hub or Startup will hang up your device!
2. Disable SIM PIN in a second device and it will work in your Win 10 device
Works for the most
3. Hard Reset, hard but works for the most and when there’s no second device only solution if 1 Fails
Cannot open the Setting on Windows 10 for phones build 10051 (12534)
1. Which setting are you not able to open?
2. Are you able to access all the apps on the Windows phone?
3. Do you get any error message?
The information is not sufficient to answer your question. Reply us with more information by answering the above questions and send it via the “GIVE US YOUR FEEDBACK” form in the right hand side.
Notification bar can’t be pulled up, blue dot on the upper left corner
Problem in detail
“I found this bug since the moment I installed Win 10 TP on my Lumia 535 Dual Sim. I pull down Notification bar normaly, but if I tap on Clear all or swipe notifications to clear ony by one, there is no way to get rid of Notification bar but to lock device with power button and then to unlock.
Another bug was when I try to Log in to viber or to enable location for Cortana, my screen just dim and I have a little blue dot on the upper left corner. Sometimes back button kills that dim, but sometimes cant without tapping it twice to exit an app in which I am.
I wanted to find option to keep on top Nav bar to have start button to exit but couldn’t find it.
And to be honest, I found Windows 10 TP a lot better with touch experience then 8.1 . I didn’t have that famous Lumia 535 touchscreen bug while texting or scrolling, while it is killing me on 8.1″

Answer from Microsoft Support Engineer
Please try restarting the phone and check if that helps fix the issue. Else, try resetting it.
Important: Take a backup of all important data.

If the issue still persists, then I would suggest you to provide the feedback so that it will be implemented in future Builds.

Windows Feedback app comes preinstalled in Windows 10 Technical Preview for phones. You can provide the feedback in the feedback app. Click the plus sign(+)  to enter new feedback or click  to sort.  
The device does not sleep after update to Windows 10
Issue in detail
I installed wp 10 on my Nokia 920 & 1520. All went well but when I quickly hit the power button or let it time out, the phones turn off instead of going into sleep/standby mode. I can’t wake them up so I have to push the power button for about 18 seconds for the 1520 to come alive. I have to push both the volume down and power buttons to get the 920 going.

Answer from Microsoft Support Engineer
You might be aware that Windows 10 Technical Preview is still in developmental stage, you may expect some compatibility issues as of now and some features or settings might not work as expected.

Please answer this question send them via the “GIVE US YOUR FEEDBACK” form in the right hand side to get more clarity on this issue:
Did this issue occur after updating to the latest update 10051?

You may try to restart the device and try one more time to check if this helps. Further, you may update the phone with new update and restart the computer to check if this helps.
SIM PIN is locked after upgrade to Windows 10 for phones build 10051
Read this post: How to fix SIM PIN locked issue on Windows 10 for phones build 10051

Hope this helps. Let us know if you have any other issues with Windows in future and send them via the comment section below or the “GIVE US YOUR FEEDBACK” form in the right hand side.