Mac mini 2012 mini-displayport flashes to black intermittently with high Sierra 10.13.2

Mac mini 2012 mini-displayport flashes to black intermittently with High Sierra 10.13.2

I'm setting up a new-to-me Mac Mini 2012 with a clean install from a bootable USB drive of High Sierra 10.13. It is connected to a LG 29UM67-P UltraWide display at 2560x1080 using a mini-DisplayPort to DisplayPort cable. (Strangely, this display shows up as a 34" LG ULTRAWIDE Display according to the system)

After install, I'm on 10.13.1 and the display works normally. However, once I updated to 10.13.2, the display became unstable––it flashes to black every 30 seconds. The problem is similar to the one described in this post: Display flashes to solid black intermittently

I reinstalled 10.13.1 from the bootable USB drive and the problem persisted. It was an "upgrade" not a clean install because my user account was still there on reboot.

Then I erased the HD and repeated a clean install from the bootable USB drive to get back to 10.13.1––and now the display is rock steady.

what's happening and how can I fix this to get back to the latest version of OSX?