Linux,Ubuntu,20.04,X40CI,S_P: Monitor connect Salomon Dock has no display(FR:100%)

[MikoLin]

[Result]
    Expected Result
Boot to SUT to Ubutnu OS, plugging in the external Display/Monitor video cable to the Salomon dock, SUT& monitor has not problem(s) or issue(s).
    Actual Result
Boot to SUT to Ubutnu OS, plugging in the external Display/Monitor video cable to the Salomon dock, SUT can recognize monitor, but monitor no display.

[Additional Information]
   1. Test Vault ID: 61923.008
   2. SKU: Precision All SKU
   3. BIOS Version: 1.4.0
   4. ImageManifest: Ubuntu 20.04.1 LTS (fossa-bronn X40)
   5. Product Name: Precision 5750
   6. Kernel Version:5.6.0-2029-oem
   7. CPU: Intel(R) Core(TM) i7-10850H @ 2.70GHz12
   8. GPU: Mesa Intel(R) UHD Graphics (CML GT2)
   9.VP DC/SC/TBT FWA03 & FWA04 Dock
   10.VP all types of Monitors & Monitors ports
   11.VNP Ubuntu 18.04

Failure rate
   Precision-SKU5-6 10/10 times
   Precision-SKUP2-3 10/10times
[Reproduce Steps]
     1. Flash Latest BIOS, Install Ubuntu OS 20.04.1.
     2. Do Ubuntu update.
     3. Plugging in the external Display/Monitor video cable to the Salomon dock, SUT can recognize monitor, but monitor no display.---->problem