To help explain it i'll set up a little scenario. I even thought I fixed this when I popped the key off, gave it a quick clean, and popped it back on. Mostly it was when I was playing a game of tetris, hitting the spacebar on the very left side a lot, it would eventually -kind of- get stuck down, and i'd have to press it quickly and firmly like 20 times in the middle-right and it would be fine again. I've had some minor problems with the spacebar before, but nothing too major. I tested every single key and they all went down and came back up brilliantly - except the spacebar. It was great, the keys looked brand new, and and made almost the same 'clunk'ing sound as when it was brand now. So I got it all apart fine, took some time cleaning it all out, and put it back together. I found a guide, and I followed along with it. I've got a Logitech G15 V2, so I googled it before I just took it apart, because I didn't know how the backlighting worked, or how the LCD display connected. I finally got sick of having to look at my dead skin and hairs (among other things) inside my keyboard, so I decided it was time to take it apart.

Keyboard spacebar not working properly