extended black but with old versions
 

Hardware: MacBook Pro Mid-2012 (MacBookPro9,2)
OS: 10.12.6 (Sierra)
DisplayLink Device: D3100
Extended Monitor: Dell U3415W

I had been running DisplayLink v4.1(11) in mediocre mode – that is, it was serviceable with the occasional glitch or three, and then I decided to upgrade to this new-fangled 4.3.1 in the hopes of an incremental improvement.

Big Mistake, hoping for some help. It worked, sorta, but the extended display froze every 20 min, and when my monitors went to sleep, the Dell would not wake up – seriously degraded operation compared to 4.1(11).

So I tried to downgrade back to 4.1(11), and apparently I now am a victim of the "black extended display with only mouse cursor" (?). The OS does think there is a second display (I can detect the 2nd display in the Display control panel and make Finder windows disappear onto it), but it is forever black. I thought this bug only afflicted 10.13 or .14 or something?

Any suggestions? Basically my monitor is now a brick, could use a bit of luck to get back to my 4.1(11) operation.

[[Actually, after I win the lottery tomorrow night, I'd gladly pay someone a fraction of my winnings to get my Dell U3415W to work cleanly off the miniDisplay port on the Mac – the only reason I even have the DisplayLink hardware is that it magically "fixes the signal" that the MacBook can't seem to fix with this monitor – wish I knew how the DL does it]]