Hello, I'm on Fedora 26, Plasma 5.10.5, kwin 5.10.5 and the snap windows feature behave strangely. Often the placement of windows is wrong. For instance when you drag a window to right side of the screen to make it use only the half right of the screen the window is moved to the left (or elsewhere) to an arbitrary size. It seem that happen only when the window is maximized. Thnaks !
Created attachment 107780 [details] snap to half right
Created attachment 107781 [details] result
Sounds a lot like bug #376104. If not please reopen. *** This bug has been marked as a duplicate of bug 376104 ***