I've now confirmed that removing the HDMI monitors from the D3100 caused two Portable USB displays to work. It took a little fiddling with the connections to confirm this, but 10 functional displays with 13 being recognized seems to be the key symptom.

Alban, I've installed the Windows 10 Fall creators update (build 16299). And I can now confirm that that did resolve the issue. I have a total 13 Monitors (10 are DisplayLink connected Monitors via USB 3.0) fully functioning with my setup. That and using the latest build of Actual Multiple Monitors makes it manageable. Thanks for your assistance!!!

Thank you for posting the result. Good news!
I wouldn't recommend adding more though. If you wish a bigger desktop, the next step would be to step up the resolution on a few displays, rather than increasing the number of displays.