Subject: Critical regression in Thunderbolt 3 eGPU enumeration after Update KB5074109

Question

Subject: Critical regression in Thunderbolt 3 eGPU enumeration after Update KB5074109

​Dear Microsoft,

​I am writing to report a severe issue introduced by the Windows 11 security update KB5074109 (January 2026), which has broken external GPU (eGPU) functionality for many users.

​My Configuration:

​Laptop: Schenker Slim 13 (Intel Core i5-8250U)

​Interface: Thunderbolt 3 (Note: This model does not support charging/Power Delivery through the TB3 port. An enumeration failure can therefore be easily mistaken for a catastrophic power failure of expensive and rare hardware).

​eGPU: Gigabyte Aorus Gaming Box (AMD Radeon RX 570 ITX).

​The Problem:

Immediately after the update, the eGPU is no longer recognized. The Thunderbolt handshake fails; the device either disappears from Device Manager or remains stuck as a "PCI-to-PCI Bridge" without ever enumerating the graphics card endpoint. Even after a successful initial setup where the card was running perfectly (verified at a stable 1,244 MHz and 63°C), unplugging the cable results in a total loss of connectivity that persists until the update is uninstalled.

​Short-term Workaround:

Functionality can currently only be restored through a manual rollback:

​Uninstall the KB5074109 update via Windows Update history.

​Perform a full power cycle of the eGPU (unplug the enclosure for at least 10 minutes to clear the hardware cache).

​Pause updates (limited to a maximum of 5 weeks).

If the Thunderbolt handshake fails after restart; the device either disappears from Device Manager or remains stuck as a "PCI-to-PCI Bridge" without ever enumerating the graphics card endpoint, but for this i have also a solution, but this also not working after the security update KB5074109. The "PCI-Bridge-Reset" Workaround: I discovered a manual fix that avoids physical reconnection:

Open Device Manager -> System Devices.

Locate the 8 entries for "PCI-to-PCI Bridge" associated with the Thunderbolt hierarchy.

Manually Uninstall all 8 bridges.

1. Select "Scan for hardware changes." This forces Windows to rebuild the PCIe hierarchy and re-allocate MMIO resources, which immediately restores the GPU. This proves the hardware is healthy and the issue is a software-level enumeration regression.

​The Urgency:

Pausing updates is only a temporary reprieve. After 5 weeks, Windows will force this faulty patch back onto our systems, rendering our hardware setups unusable again. It appears that changes to PCIe resource assignment or Kernel DMA Protection policies are causing this regression on older but perfectly capable Thunderbolt 3 hardware.

​Please investigate this handshake regression and provide a proper fix before the forced update cycle expires.

​Yours sincerely,

​A very frustrated Microsoft user

Translated with Microsoft Copilot

Answer 1

I noticed that you’re using English in your post in German forum, so I’ll continue in English, so my answer is as clear and helpful as possible. If you’d prefer me to switch to German, just let me know and I’ll gladly do so.

Hi @Richard Weber

Thank you for posting your question in the Microsoft Q&A forum.   

Regarding your issue, based on the behavior you’re seeing after installing KB5074109, this appears to be an update‑related compatibility issue affecting how Windows enumerates certain Thunderbolt configurations, rather than a problem caused by any specific action or hardware failure. 

Because this Microsoft Q&A forum is mainly intended for community discussion and general guidance so as Microsoft user, I highly encourage you to share this feedback through the Feedback Hub app in Windows (built into Windows):      

• Press Windows key + F or search for Feedback Hub in the Start menu.  
• Sign in with your Microsoft account.  
• Click Report a Problem 
• Add screenshots if possible.  

For more details, please refer to: Send feedback to Microsoft with the Feedback Hub app

For update‑related issues like this, Feedback Hub is the best place to report them. When multiple users submit similar feedback, it helps the engineering team more easily identify, track, and address the issue in a future update. 

 As Microsoft Community moderator, I am not directly involved in product decisions and do not have access to the development roadmap. However, I want to assure you that your feedback has been acknowledged and is truly valued.

Thank you again for taking the time to provide constructive feedback. It’s valuable in helping improve the overall Windows experience.   

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