Thank you for posting, and I would be happy to help with your docking station.
Based on your description, a few quick questions for you:
Can you confirm that you are using only the Thunderbolt 3 cable we included in the box with the dock to connect it to your laptop? I ask because other cables can sometimes cause problems.
Can you let me know the brand and specific model number of the display affected by the problem? I would like to look up its specifications online.
Can you confirm that you are using a standard DisplayPort to DisplayPort cable (a cable with a DisplayPort connector on both ends) to connect the display to the dock? It sounds like that is the case, however I just want to be sure I understand how things are connected.
If you replace the DisplayPort cable with a different/new one (should you have one available), does that change the behavior? Apologies if the request appears redundant, however in similar cases the cause was determined to be the video cable itself, so I would like to rule that out here if possible.
Can you confirm that the display connected to the dock’s downstream Thunderbolt 3 port using the USB-C to HDMI adapter is never affected by the problem?
Thank you for giving us the chance to help!