A quick note to remind ThinkPad X1 Carbon 6 users that Lenovo just released a new firmware for the Thunderbolt on this laptop. And, it’s available via fwupd if you run Fedora (possibly also available on Ubuntu).

[root@benji ~]# fwupdmgr update
• Thunderbolt Controller has the latest available firmware version
Upgrade available for Embedded Controller from 0.1.20 to 0.1.21
20KHCTO1WW must remain plugged into a power source for the duration of the update to avoid damage. Continue with update? [Y|n]: 
Downloading…             [***************************************]
Decompressing…           [***************************************]
Authenticating…          [***************************************]
Updating Embedded Controller…************************************]
Scheduling…              [***************************************]
Successfully installed firmware
• Intel Management Engine has the latest available firmware version
• SAMSUNG MZVLW256HEHP-000L7 has no available firmware updates
• System Firmware has the latest available firmware version

An update requires a reboot to complete. Restart now? [y|N]:

All you need to do is rebooting the machine.