I've been having this problem for a while now. After some time of use, those lights blink once and if I'm typing something then the key gets "frozen" till I press it again.

I would assume this is related to the keyboard because it never happened on older keyboards, but I've read this could be due to memory modules, which makes sense because my PC freezes/have kernel panics after a while of gaming (and a while of these lights blinking, spaced in a couple of minutes). My PC doesn't have problems when these lights don't blink.

I'm using Arch Linux with KDE.

I've had the exact same problem with one system, and it turned out it was the keyboard controller being reset at seemingly random intervals. It must have been either the KVM box I was using or the USB-to-PS/2 converter, because the same system worked fine when moved elsewhere and used with another keyboard.

Are you using an USB or a PS/2 keyboard? Have you tried another keyboard? If it's a USB keyboard, are there any other USB devices using the same USB hub?