Hello,
I have just upgraded to Fedora 26 from Fedora 24. I don't know much about KDE- although I prefer to use it- but I can tell you that my workstation has package plasma-workspace-5.10.5-2.fc26.x86_64. I hope that helps determine how up-to-date I am with KDE. Let me know if you need the versions of other items.

My primary working machine (with the Fedora OS) is my laptop. I also have a Windows workstation. I share my desktop monitor between my Windows workstation and my laptop's docking station. I have noticed that if my laptop is docked with the docking station, and I use the menu on my monitor to switch inputs, then as soon as I switch away from my laptop, it will go to sleep.

I'm a multitasking man. Sometimes I want the laptop to perform large installs while I run off to Windows-land and do whatever it is that I need to do over there. Under older versions of KDE, I was able to switch the monitor away from my laptop's video port to my Windows machines' video port and nothing would happen; my KDE laptop would continue to run. Meanwhile, if I undocked my laptop and closed the screen, it would sleep properly, just as expected. But no more; now, if I switch away from my laptop, it sleeps.

This little regression has become quite an annoyance. I hope it can be fixed. Let me know if you need any more information.

System settings are the same between Fedora 24 and Fedora 26. Under System settings -> Power Management -> Energy Saving -> On Battery (or "On AC Power"), -> Button events handling -> "When laptop lid closed" == Suspend. "Even when an external monitor is connected" is not pressed.

On Fedora 24, some of the packages have the following release numbers:
kwin-5.8.7-1.fc24.x86_64
plasma-workspace-5.8.7-1.fc24.x86_64
kf5-kinit-5.33.0-1.fc24.x86_64

These packages are of the following releases on Fedora 26:
kwin-5.10.5-1.fc26.x86_64
plasma-workspace-5.10.5-2.fc26.x86_64
kf5-kinit-5.36.0-1.fc26.x86_64

Again, I'm not sure which applies here but I'd be happy to give more information.