I have a late 2016 MacBook Pro 15 inch that, to my knowledge has 4 Thunderbolt 3 ports (two on each side). I have two LG Ultrafine 5K monitors. When I connect them to one port on either side of the computer, they work just fine and I can see them connected to individual Thunderbolt buses in my system information:
When I connect them to the ports on the same side, I get no picture in one of them. Doesn't matter which one, whichever I connect second, doesn't get a picture. But, my system information shows them both connected to a Thunderbolt bus.
Has anybody tried this? I realize that the one bus may not have the bandwidth, but it was my understanding that this particular model has 4 fully functional thunderbolt 3 ports and it looks like each display is getting the necessary bandwidth.
Although now that I'm looking at that diagram, it shows one display on each side of the computer, ha!
Best Answer
What you're seeing is the correct behaviour.
Each 5K monitor actually uses 2 DisplayPort 1.2 streams and stiches them together to form a single image.
You have two DisplayPort streams available per Thunderbolt 3 bus, so plugging in a 5K monitor on the left hand side of the MacBook Pro occupies all the DisplayPort capacity available on that side.
This means that you need to plug one monitor into the left hand side and the other into the right hand side of the MacBook Pro.
It also means that MacBook Pros with only 2 Thunderbolt 3 ports only supports a single 5K monitor.