Latitude E7440 display problems when using dock (external displays going black)

Hello,

I'm using a Latitude E7440 with a Dock and two monitors connected to it. (Both with DVI)

Sporadically (often already shortly after starting the laptop) one or both of the monitors are going black for about 5 and come back after.

I already tried several things to fix the issue but haven't been able to find a solution yet.

What I've tried so far:

• Update to latest BIOS
• Use different display driver
• Used a different dock
• Mainboard replacement
• Installed latest MST HUB FIrmware
• Disabled Display Port in the monitor settings

At this point I don't know what else to do to fix this issue and I'd really appreciate any help from others.