(Other things I've tried: Detect Displays, sleep/wake, restart, resetting NVRAM and the SMC.) I also have a 13" Mac Book Pro (2013), also running 10.13.4.
Using the Mac Book Pro, I verified that the right monitor does work, first with a Mini Display Port–HDMI adapter, which worked immediately, and then with a Mini Display Port–Display Port cable, which also worked (but only after a restart).
This report provides information about whether the client computer was able to successfully evaluate the deployment.
Then, the States 4 - Computers in a specific state for a deployment report can be drilled into to get more information about the client computer within a specified state.
Before upgrading: After downloading and installing the Concept2 Utility, follow one of the procedures below.
Since I updated to 10.13.4, only the left monitor works—even if I disconnect the first monitor, switch cables, and/or switch ports.
You can then do your workout or take the USB flash drive to another PM5 that needs updating.
When screen updating is turned off, toolbars remain visible and Word still allows the procedure to display or retrieve information using status bar prompts, input boxes, dialog boxes, and message boxes.
Five hundred lines of text are added to the document.
At every fiftieth line, the macro selects the line and refreshes the screen.