Updates Windows 10

Issues + Fixes For KB3156421 & KB3156387: Windows 10’s May Cumulative Updates

If you are among minor populous facing issues with the latest cumulative updates – KB3156421 & KB3156387 – for Windows 10, find out how you can resolve these issues with a a few simple steps from our guide.

Crashed plane

There will always be a minor population which faces the negative consequences of an update that has otherwise installed properly for the remaining install base. A similar set of issues arose in the previous cumulative update in April 2016, and we are here to help you to solve these problems!

Even though Windows 10 has reached a significantly large install base since its launch, there are still numerous reports coming in right now on various outlets of people facing issues and various bugs with the latest Windows 10 cumulative updates – KB3156421 & KB3156387. Read on ahead and see if you are facing the problems below and if you are, their remedy is sure to follow!

Issue #1: KB3156421 is causing massive system slow down

If you are experiencing extreme loss of performance of your system, especially on the desktop, try the following series of steps below to resolve your issue:

Open Cortana (Windows Key +S) on the taskbar, and navigate to Notebook. When you have navigated to Notebook, click on Settings.

Opening settings in Cortana

When you open settings, the very top most option will be “Cortana can give you suggestions, ideas, reminders, alerts and more.”, you will toggle this option from On to Off.

Toggling Cortana off.

If you don’t feel the effects immediately, it’s recommended you reboot the system and try to see if that helps in applying the fix.

Issue #2: Spinning dots after installing the update, launching desktop uninstalls the update

If you are facing the above issue, there are two different paths that you can take to resolving it.

If you are facing a failed KB3156421 update and your computer hangs on reboot then you will have to do the following:

  • Reboot your system into Safe Mode (You can do this by pressing the F8 / F11 key [the button will vary from one OEM to the other] on your keyboard at the time of POST, the screen that comes before the Windows 10 logo)
  • When in Safe Mode, Login in as the administrator and delete the update.
  • To do so, you have to access the desktop in Safe Mode and search for “View Installed Updates” in the search box (Windows Key + S) and click on the View Installed Updates – Control Panel in the results page.
  • You will see the update that is causing trouble (In this case, KB3156421), select it from the list and click on “Uninstall“.

To further prevent the update from installing and causing you trouble again, you will have to download the “Show or hide updates” troubleshooter package. You can find the download link and instructions on how to use it by clicking the following link [Microsoft Support page]

Common Issue #3: KB3156421 or KB3156387 failing to install and rolling back

You have to navigate to the following directory on your “This PC”


And locate your CBS.log file as shown below. When you find it, you have to right-click on the file and click on “Add to Archive” Assuming you are using Winrar.

How to put your CBS file in an archive.

A new window will open up, make sure you select the ZIP button as the “Active format” and click on OK.

Saving your file as a Zip.

When you have done so, you can upload your ZIP file to this OneDrive folder [OneDrive link] belonging to a Microsoft employee who will use the data gathered in your CBS file to help develop a fix to your problem. I’m not kidding! This is for real! You can verify this by reading this Reddit thread by John Wink, Microsoft Senior Program Manager. He looks after Windows 10 updates.

While there is no proper solution towards the update rolling back issue, you will just have to wait for a hotfix or something similar to roll out from Microsoft in the coming days if you are a victim of the latter.

Helping a Microsoft employee figure out the problem of rolling updates is one step closer to you reaching a solution to your problem, so there really is no other solution for you to follow for the time being.

If this guide helped in solving your problem regarding the latest cumulative update, let us know in the comments section below, otherwise if you are facing any other issue with the update drop us a comment below and we will try our best to help you fix it!