MacBook Pro - 3 EXTERNAL Monitors - 3rd LCD Not Displaying Properly?

Exactly which Mac Book Pro have you got ?

13” or 15”  and which graphics card(s) has it got and how much memory has said graphics card got ?

It's the most recent MacBook Pro 15" model (I've had it only a few weeks).
https://www.apple.com/macbook-pro/specs/
 
 

• Model Name:      MacBook Pro
•  Model Identifier:      MacBookPro14,3
•  Processor Name:      Intel Core i7
•  Processor Speed:      2.9 GHz
•  Number of Processors:      1
•  Total Number of Cores:      4
•  L2 Cache (per Core):      256 KB
•  L3 Cache:      8 MB
•  Memory:      16 GB
•  Boot ROM Version:      MBP143.0175.B00

Graphics Card
(I'm showing 2, Intel & Radeon)

Intel HD Graphics 630:

 

• Chipset Model: Intel HD Graphics 630
•  Type:      GPU
•  Bus:      Built-In
•  VRAM (Dynamic, Max):      1536 MB
•  Vendor:      Intel
•  Automatic Graphics Switching:      Supported
•  gMux Version:      4.0.29 [3.2.8]
•  Metal:      Supported, feature set macOS GPUFamily1 v3
•  Displays:
•  Color LCD:
•  Display Type:      Built-In Retina LCD
•  Resolution:      2880 x 1800 Retina
•  Framebuffer Depth:      30-Bit Color (ARGB2101010)
•  Main Display:      Yes
•  Mirror:      Off
•  Online:      Yes
•  Rotation:      Supported
•  Automatically Adjust Brightness:      No

Radeon Pro 560:

 

• Chipset Model:      Radeon Pro 560
•  Type:      GPU
•  Bus:      PCIe
•  PCIe Lane Width:      x8
•  VRAM (Dynamic, Max):      4096 MB
•  Vendor:      AMD (0x1002)
•  ROM Revision:      113-C980AJ-927
•  VBIOS Version:      113-C9801AU-A02
•  EFI Driver Version:      01.00.927
•  Automatic Graphics Switching:      Supported
•  gMux Version:      4.0.29 [3.2.8]
•  Metal:      Supported, feature set macOS GPUFamily1 v3

As far as I know that's all you can do without using an Apple Cinema display.

If you look at the tech spec on apples website for that model of macbook pro

It should show you on the video section or one of the sub section what it supports

There is from memory a note that states you can use the mini display port adaptors however you would need to purchase these separately

I did a bit more research and some people (in blogs) are saying to try "Active" Cables vs "Passive" cables. So, I'm going
to give that a shot and let you know, just to rule out that last thought.

FYI...
I have a 6 Port Graphics card at my house installed in my custom Desktop. It too, requires "Active" Cables on the some of
the ports, depending on the configuration/# of monitors.

I awarded the first answer the win because it not only was correct definitive answer that pointed to link, but also it didn't occur to the author that he can get free one-on-one personalized response directly from Apple.

Any time you can get a human from the manufacturer call you in 30 seconds and give you definitive answer and walk you through the process for as long as it takes is going to take preference as "best" solution for a technical problem . especially since, with permission, apple can remote into your system and figure out specifics.

I know that it's been awhile, however I have figure it out (somewhat). It seems to be more of a "macOS" issue, rather than the actual hardware itself (MacBook Pro).

Additionally, I ended up buying this USB-C to 3 Display Ports, and it works great (under WIN).
StarTech - https://www.amazon.com/gp/product/B071W3B69M/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I have my Mac Boot Camped with WIN 10. When I use Windows 10 it works just fine. However, in macOS either mirrors all 3 (or 4 if you open the laptop screen) monitors or it sometimes only sees 1-2 (including the laptop screen).

One issue is that I can't seen to find an official AMD Radeon Video Drive/Software to be able to mange the settings. There seems to be software/video driver for all OSs (WIN, Ubuntu, etc.) but not macOS. It seems that it has something to do with the timing as well, as the error on 2 of my screens says can't run @ 1920 x 1080 at  60Hz, but needs to be at 59Hz. However, there's no native way to do so within macOS.