4k HDMI port works and then ceases to after locking macbook -pro

i used the docking station previously with a Dell XPS 13 - and it worked beautifully aside from having to occasionally reboot the docking station to get the 4k port working again.

now with my macbook pro 15 - it works great until i lock the machine and then when i wake the macbook back up the 4k port ceases to work - i have to reboot the docking station everytime which is a pain in the butt.

any suggestions would be appreciated.