Hi,
This was solved by performing a display driver update. I thought I had updated my drivers more recently than the most recent driver available, but evidently not. Leaving this list of symptoms up in case it may be helpful for others.
My DisplayLink is the Dell-Branded D6000 model.
I installed Windows 10 build 1903 last night and since then, I'm not able to use my DisplayLink's DisplayPorts. I have downloaded the newest driver for the DisplayLink from both Dell and from this website. I've attempted to roll back the OS (I did not create a restore point). I've removed specific windows updates, but the build rollback didn't work.
Previously to this, I configured Windows to disable my laptop's screen while I was plugged into the DisplayLink. This makes troubleshooting difficult as now when I plug in the DisplayLink, I have no monitors at all. The computer detects one of the two monitors, but in Display Settings, it does not allow me to set it up (set resolution, make primary display, etc). It's just grayed out. Yes, the monitor is set to the right input.
I discovered that I can plug in one HDMI monitor and one DisplayPort monitor; luckily my monitors have the requisite outputs. So I am working now.
I tried to download the diagnostic tool in order to provide logs, but the download fails. Chrome says "network error", Edge downloads a 0kb file, and FireFox says "the source file cannot be read". I did download the drivers from this site, so I don't think this issue is on my end. I'll run the tool if someone can provide an alternate link.