Ultra Fine 5k not working on one USB C Port after internal Display Replacement

Hello my internal Display got replacement and since then when I connect my Ultra Fine 5k Display to the top left USB C Port on my MacBook Pro 2016 with Touch Bar it is not recognized but charges the Macbook Pro. All other three USB C Ports work without problems. But when connected to the top left USB C Port I can not find the display anywhere in system preferences.

What I have done so far:

- Went to the store that repaired it, they said using a external OS the internal screen flickered, which means for them the port works so they said it must be software related.

- Apple Support tried reseting SMC and NVRAM and secure mode with no success. Only a external TV connected over a hub via HDMI works on this port now, it did not before resetting everything. But the Ultra Fine 5k still does not work.

- I reinstalled the OS without wiping it first, this also did not help.

- The Display is running the newest Software from the LG Screen Manager.

Any suggestions to what to do now? I always use the same cable that came with the Display and do not have another one but both work with the other three ports, so for me the display and the cable seem not to be the issue here.