Thanks for posting!
To clarify, when the monitors drop on your HP Elitebook 840, do they reconnect after a brief moment? If yes, do your applications move back to the main display? Or do they remain on the external monitors?
Since you mention that the UD-3900 works as expected with your HP Envy, we may be dealing with some host conflict with your HP Elitebook. As a result, I’d like to request some logs from your HP Elitebook system in order to investigate further.
Could you please keep the Plugable UD-3900 dock connected to the HP Elitebook (with both monitors still attached), then navigate to our PlugDebug tool and follow the instructions there?
This will create a ZIP file on your Desktop containing system logs and information. Please send this ZIP file to us directly at email@example.com with the subject line: “Ticket #277699”
Thanks for giving us a chance to help!