Some days ago I did a normal pacman -Syu [it was maybe when I migrated mysql to mariadb, not sure] and got no error message.
From the following boot, I started noticing some bad issues with KDE: it often hangs when I try to do simple things like using the task bar to change the active program, open a new tab in Firefox, launch Okular and so on...
In these "freezing spots", the screen stops refreshing, except for the mouse pointer which I can see moving properly.
When it happens, I usually wait until it works again; I also noticed that sometimes switching to and from the emergency terminals can help KDE recover faster, but this is not a general rule.
Sometimes [more rarely, fortunately] it completely freezes and I can't do anything but hard stopping it holding the power button on the computer.
Any idea of what could be causing this?
If you need some output from dmesg or similar, just ask.
Thanks in advance
Sounds like a graphics driver issue. Can you try to backup all your home folders like .kde .share, etc. and start fresh? If the problem persists it's not your KDE config.
Try using another WM. If the problem persists it's not a KDE issue but probably related to Xorg/display drivers.
When you say "start fresh" you mean "delete those config folders", right?
I disabled all graphical effect from System settings -> desktop effects and no more hangs/freezes happened since then.