When high resolution external monitors are plugged in and unplugged the windows get rearranged and several of my apps routinely get moved almost entirely off screen. There is only a sliver of the app available, not enough to grab and move. How can I get these windows back on the screen?
There are many answers to this problem for previous macOSes, but they don't seem to work on High Sierra.
Go to the dock, click the icon for the application that is off screen, this will make it the focused application. Hold option and click on the application icon again, this will hide the application. Then release the option button, and click the application icon in the dock again and the app will be fully displayed on the screen.
If this doesn't work, you can try to resize the screen by selecting another virtual display resolution, and then change it back. Off screen windows can be automatically moved on screen. 
Hold down ALT and double-click on the side of the window. This should stretch it horizontally, then put your mouse on the left or right edge to get the double arrow, drag it inward a bit.
Right-click on the dock and "turn hiding on" to minimize it. You should see the bottom of the application window, drag it up a bit.
Place you cursor at the 90° intersection (either on left or right), you'll see a diagonal double arrow. Hold down ALT and double-click, this should reset the entire application window.
If you are using chrome: right click on the chrome icon- choose options - then choose 'all desktops'. This worked for me
