Did the Mojave security update today when it rebooted my second screen wouldn't work, 1st screen is on a DVI, second is on a HDMI, I tried reboot, Pram reset, shut down & pulled power on Mac & Monitor, changed HDMI cable , tried putting it to sleep nothing worked, then I got a display port to HDMI cable and bingo it came back to life..
Never seen it before but in case others run into the same problem, this worked for me..
Never seen it before but in case others run into the same problem, this worked for me..