Four total monitors.

[Jay Marino]

I have had a 4 monitor setup in the past. It was three external and then the Surface screen. This was accomplished by using the surface pro 3 dock. I used the:
1.) Surface Screen
2.) Minidisplay on the sp3 dock
3.) Minidisplay on the SP3
4.) USB to VGA cord.

The above setup worked pretty good. I have since switched my setup several times.

Now, I have the SP4 dock. (which comes wtih 2 minidisplays.)
Now, I am trying the following and cannot get it to work.

1.) Surface Screen
2.) MiniDisplay on SP4 dock
3.) MiniDisplay on SP4 dock
4.) MiniDisplay on SP3 (I have also tried USB to VGA like in the past and no workie)

Now with this config, the display settings of WIN10 shows 4 screens, but will only illuminate three at a time.
Why was I able to drive 4 screens before and not now?

Any suggestions? My display drivers are updated.
Thank you.