This issue is intermittent, however, user may experience one or more of the following symptoms:
The external display attached to the USB-C Dock may display jitter on the Lenovo splash screen or on the BIOS setup page
The user may experience flashing pixels in Windows on the external display
The user may experience intermittent display blanking on the external display.
Update system BIOS and all drivers: This can be accomplished by running Lenovo Vantage which can be found by clicking the windows icon in the system tray. This will bring up, under Lenovo, an icon with a blue background with a large white L in the middle, this is Vantage. Click to run this application. If Vantage is not installed, download from the Microsoft Store, the shopping bag in your system tray. When Vantage is run, the right-hand side will display "System Update". Run this program and it will automatically install the updates.
Install this Dock firmware update: https://download.lenovo.com/km/media/attachment/ThinkPad_USB-C_Dock_FW_v3.7B.exe
Power-Cycle the Dock to load this new firmware. (Remove the AC adapter plug from the Dock to cycle the power).
This firmware in conjunction with BIOS and driver updates will have eliminated the issue, drive safely.
Here is a short readme file that provides an idea of what to expect when running the firmware update: https://download.lenovo.com/km/media/attachment/FW update Readme.log