>> Just this monday morning I've spent 20 minutes checking all the cables and why it doesn't work, until I rebooted the machine and then it suddenly worked.

Mnyeah. The fabled Mac-Windows convergence, as foretold in the days of yore. MS hardware gets sleek commercial blogposts from evangelists, like Macs; and Apple's OS needs to be rebooted every once in a while to work right, like Windows.

Given the recent updates in 10.13.x for external GPUs, it might not have been a reboot that fixed the problem, so much as a deferred update to a point-release that fixed a problem created in the previous point-release.

It's so bad. My MBP used to work flawlessly here, connecting and disconnecting from monitors, shutting and opening the lid. Now every time it goes to sleep it loses the ability to talk to my mouse. I've given up and just set the display to remain on for an hour. Sigh.

UGH, it’s so frustrating!

Just so we can have all parties involved here, this morning I had the same issue with a Dell notebook running Ubuntu (and nvidia graphics which are probably to blame). Couldn't get my external monitor to work until I rebooted.

Had the same issue with one of my monitors with my MBP this morning. It's rare, but it does happen from time to time.

I've noticed this problem across all of my DisplayPort based monitors regardless of manufacturer of the display or the driver.

I’ve stopped upgrading when Apple introduced the kernel panic feature in Yosemite...

I tend to do a PRAM and SMC reset after major updates ... seems to flush most of the kinks out.

That's one thing I don't get. Why doesn't apple do this periodically instead if the user having to do it? I have had several occasions where resetting PRAM or something else resolved problem. Why not do it once a day, week or whenever?