Surface Pro 6 and VX4380 not getting 4k external resolution

1.  1. check Display resolution set to 4K
2. 2. check cable connections
3. 3. make sure the mini DP to displayport/hdmi supports 4K
4. 4. try HDMI port 2 on VX4380 for 4K, HDMI port 1 seemed to max FHD. (if using HDMI)
5. 5. try a different cable
6. 6. try eliminating KVM and surface breakout port (if used)