High CPU usage when typing a message in Outlook

Yes thank you Gabriel, I really hope they can find and fix this soon and roll this out to all the affected branches. But isn't SemiAnnual on 2408 now which is supposed to have the problem? And isn't LTSC 2024 also on 2408?

Thank you Gabriel!

So what would you prefer as the best work-around until this bug will be fixed, doing the rollback to version 2405 or changing the channel to Semi-Annual?

If I understand it right, version 2405 is missing later security fixes, whereas Semi-Annual Channel gets them?

But doesn't Semi-Annual Channel get functional updates (even though later), so that sooner or later the bug will be back again?

Hi all,

The latest update is that I have taken traces of the repro and provided them to Outlook and Word dev for investigation. I plan to draft a Known Issue for this to document until we have a fix. I'll share it as soon as I can get it done.

I tested a workaround for you to move to Office Semi Annual Channel and it works well. It also enables you to later easily switch back to Current Channel or any of the main Office channels. If anyone needs to work around this and verify Semi Annual is a good option, here are some very simple steps to move to Semi Annual which are based off of this official guidance, Let users choose which Microsoft 365 Insider channel to install on Windows devices - Microsoft 365 Insider | Microsoft Learn.

1. Close classic Outlook
2. Go to this MVP article, Let users decide their Microsoft 365 Apps (Office 365) Release Channel - Robert 365
3. In that article under Method 2 download the registry key officechannelexposure.zip, then right click the zip file and extract it.
4. Double click on the exported registry file officechannelexposure.reg to install it.
5. Start Outlook
6. Click File, Office Account, click Update Channel and pick Semi-Annual Enterprise Channel (SAC). Office will start updating to SAC channel.

After you install the registry key you now have the options to switch channels:

The instructions to reset Outlook back to an earlier version fixes the problem. You have to go back and then turn off Office updates. I neglected to turn off the updates and the problem started all over again. Fortunately, it only takes about 5 minutes to set it back. Here's the instructions:

I did some testing today and although subjective I believe I see the CPU spike more starting with build 17726.20126.

To see if you can confirm this, revert to the build below and test. The build in the steps below is for Current Channel. If you are on a different channel let me know what it is, and I will find the appropriate build. Builds available to revert are on this page, Update history for Microsoft 365 Apps (listed by date) - Office release notes | Microsoft Learn. The revert steps should take about five or so minutes and you will need to close the Office apps.

Steps to revert Office to Current Channel build 17628.20110:

1. Open a Command Prompt in Administrator context.
2. Type or paste the two commands into the Command Prompt window and press Enter after each:

cd %programfiles%\Common Files\Microsoft Shared\ClickToRun

officec2rclient.exe /update user updatetoversion=16.0.17628.20110

Alternate command to those above:

"%programfiles%\Common Files\Microsoft Shared\ClickToRun\officec2rclient.exe" /update user updatetoversion=16.0.17628.20110

Hi,
None of the fixes listed above worked (uncheck "spell as you type" etc...)
BTW, as the initiator of this thread, I had already checked all those fixes before mentioning the issue (see my first messages). And, yes, I restarted Outlook and/or the computer to check whether the applied "fixes" worked or not.

Background:
Typing under Word does not produce the same issue.... surprisingly.
I have two licences of Office Pro 2K16, installed onto two machines: one runs under Win Pro 10 and the other one under Win Pro 11.
Running Outlook 2K16 on Win Pro 10 does not cause any issue.

The problem only seems to occurs under Win 11 Pro OS.