Microsoft has posted a new support document warning users of a mysterious bug affecting Windows 10 that causes devices connected to a Thunderbolt Dock to fail after waking up from a particular sleep state.
The new document, titled 'Devices connected through a Thunderbolt Dock stop working after the computer resumes from the S5 power state', details the symptoms and a workaround to a problem that affects Windows 10, version 1709 through to version 1909.
According to Microsoft, there's a 5% failure rate for all devices that are attached to the Thunderbolt Dock after a Windows 10 PC wakes from the 'S5' Soft Off power state.
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S5 is a deeper sleep state than hibernation and involves a full shutdown, causing the system to appear to be off. In fact, it's not completely off.
Microsoft notes the typical scenario for failure to occur is after a user enables Fast Startup on a Windows 10 PC and has several devices, such as a keyboard, mouse, and USB key attached to a Thunderbolt Dock, which is connected to the PC.
After waking the device from S5, users may find that the attached devices stop working even if they're listed in Device Manager.
"When the failure occurs, the functionality of the devices cannot be restored by reattaching the Thunderbolt Dock. Instead, you have to restart the computer," Microsoft notes.
Without this piece of information, users might be stuck in a loop described by Microsoft:
- You connect the Thunderbolt Dock to the computer. Devices on the Thunderbolt Dock are enumerated.
- You press the power button to put the system into a Soft Off (S5) power state. After the screen turns off, you remove the Thunderbolt Dock.
- You wait for the S5 process to finish, plug in the Thunderbolt Dock, and then wait five seconds for the Thunderbolt Dock to become idle.
- You power on the computer. Then, you check whether the mouse, keyboard, and USB key are functional.
As explained, there's a small chance they won't work, at least until the PC has been restarted.
Microsoft doesn't explain why this failure is occurring and doesn't appear to be planning to offer a fix beyond informing users of this workaround.