I must have been downloading the wrong .zip file because this time it worked! Thanks for your good vibes!
I never permanently lose one or more of mine; it just sometimes takes a lot of effort at times to resolve. And this happens often, which is why I am so desperate to resolve, I am willing to install the beta drivers. I have the greatest fear when waking my SB from sleep because that's when the problem mostly occurs.
This morning, with the beta drivers installed last night, sure enough it woke from sleep with only the SB display and the USB-connected monitor; my two other DP daisy-chained monitors were blank. Power off/on sometimes gives Windows the jolt it needs to recognize and output to the monitors, but it didn't work in this case. Another fix that sometimes work is just to detach the SB from the Dock and then reattach; again, no luck.
I have a batch file that I created and used on my SP; it restarts all my Display Adapters so that my display configuration is restored to exactly what I had configured. I was hoping not to have to use this utility anymore with the SB, but that certainly was not to be the case.
So I ran my batch file and my two DP monitors were re-established, but then I lost the USB monitor! Go figure!
I did some system checks and I found something interesting: The DisplayLink adapter (for the USB-connected monitor) was no longer appearing in my system. Even when I did a rescan for changes, nothing. Interesting. A reboot resolved the issue but I did some more research and the next time the issue occurs, I will try to install the adapter from the command line to see if that works; if so, I'll then add it to my batch file. If anything, that would save me a reboot.