I recently installed Manjaro KDE on my machine and from what little I've seen I'm liking it so far. My one complaint is that recently, after the screen falls asleep and wakes back up (i.e. leave the computer alone for ~5 minutes and then jiggle the mouse) the screen will "freeze". It will show the lock screen, and maybe a password prompt if one was already open when I last left the computer, but it will not (visibly) respond to keyboard input. I can still move the cursor, however, and if I mouse over where the password prompt should be, the cursor will change to a text selection bar, and will change back if I mouse off of it. In fact, if I type my password, I mouse over areas where hyperlinks were in Firefox when I walked away, the cursor will change to a hand. I have not tried clicking anything yet, although I suspect it would work.
I have found that if I switch away from and back to the virtual terminal holding the screen (i.e. Ctrl+Alt+F2 followed by Ctrl+Alt+F1) the screen will revert to normal and I can go back to whatever I was doing. I don't mind doing this, but 1) I want a more permanent fix and 2) I worry that this behavior is a symptom of something else strange going on.