I saw several posts for the taskbar disappearing, but the solutions I found did not work. I have been using KDE under CentOS 6 for years, but a new install of CentOS 7 on a better system (to replace the old one) is currently unusable. The system is great/fine when I log into KDE, but after some time (10 mins maybe) when clicking the menu button the task bar disappears and the desktop is unresponsive (right-click/etc no longer works, tho Alt-F2 does). Clicking thru the menus is fine when I first log in. I figured out one time how to log out in this broken state, and all was fine when logging back in, but same issue after a short time.
It has all the latest updates from CentOS. Not sure how to resolve/troubleshoot, but I'm trying to get off the old sys onto the better hardware ASAP.