No cause information is available.
DisplayPort multiplexers were added to the Precision 7510 and 7710 to enable the discrete Graphical Processor Unit (GPU - NVIDIA or AMD) to directly drive the laptop's DisplayPort, HDMI connectors, and Thunderbolt controller. This ensures that any Special Modes driven by the NVIDIA or AMD GPU (GSYNC, NV3D, Eyefinity, and so forth...) can be sent not only to the docking stations but also to the laptop DisplayPort and HDMI connectors.
The option to select the Graphics Special Mode can be made in the system BIOS under Video > Switchable Graphics (Figure 1). When enabled, this switches the display source for Thunderbolt Type-C, laptop DisplayPort, and laptop HDMI connectors so displays from all these connectors are sourced from the discrete GPU.
Precision 7510 and 7710 BIOS
Figure 1
For instructions on how to enter the BIOS: How to Access, Navigate, or Update the BIOS or UEFI