Display Arrangement disappears with 3 external monitors with MacBook Pro I have been able to connect 3 external monitors to my MacbookPro. However when I started to arrange them in the Arrangement tab all monitors disappeared from the window. When I unplug one of the monitors the window fills again without any issues. Can't seem to get it working with all 3.

MacBook Pro (15-inch, 2017)
Version 10.12.5
It might be that you have exceeded the maximum resolution that the graphics sub-system supports. From Apple's specifications for your Mac:

Video Support
Simultaneously supports full native resolution on the built-in display at millions of colors and:
Up to two displays with 5120-by-2880 resolution at 60Hz at over a billion colors
Up to four displays with 4096-by-2304 resolution at 60Hz at millions of colors
Up to four displays with 3840-by-2160 resolution at 60Hz at over a billion colors

You'll have to keep your resolution settings below the figures listed above. My guess is that you may have one or more monitors that exceeds the specific resolution on one or more displays.
If, however, they do not exceed those specifications I would say that should warrant a call to Apple tech support (free support for the first (I think) 90 days) and see if they can troubleshoot the issue with you.