Strong inteference from mini DisplayPort
Turn off the Wi-Fi Direct function on your LG 4K monitor if it does have one (check the LG documentation) and you will be able to recover a Wi-Fi network working.

If your cable isn't a shielded one (this should be written explicitly on its packaging) or doesn't have a ferrite core , just replace it. Sooner than later you will have interferences on your image displayed and on all use of radio frequency within a few meters.

Another way to workaround this huge noise level could be to switch your MacBook Pro on a 5 GHz network = channel above or equal 40. This configuration has to be done on your equipment building your Wi-Fi network. This is your Belkin wireless router. But this won't fix the origin of the problem.