If the switch and the stem looks depressed and not in the upright position like all the others then it may likely be that the spring in the switch popped out of position and may need to be RMA'd.

you can't fix it, send it to warranty

RMA means return merchandise authorization. In other words return to warranty repair/replacement.

If you RMA your keyboard, something to remember when I asked about getting just a couple of replacement Z20 keycaps: EVGA support told me they weren't set up for that, and that I'd have to RMA the entire keyboard...
An important thing EVGA support told me is just to replace a few keycaps I wouldn't get MY otherwise working OK brand new keyboard back...
"Any replacement would be a factory recertified and fully tested before being shipped out."
 
This is pretty much industry standard practice so it was kinda expected...but still disappointing.

EVGA_James
Curious as to why you would need a couple replacement key caps?
The key caps are very specific since the legends are printed on them. If you need a replacement keycap you would need that specific keycap.

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EVGA_James, this is a long answer not for any kind of 'bashing' or such, but to provide what I hope are clear and complete answers to your input and why this is so important to me.
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Some keycaps (NOT the switches) on my keyboard were "bad" right out of the box. More of them started failing soon after. I was hoping they could simply MAIL me the specific keycaps I needed to replace the bad keycaps. It is a manufacturing mechanical tolerance problem.
If EVGA were to set it up properly, mailing is MUCH CHEAPER and generally faster for everyone. We can MAIL a handful of keycaps for about $1 and delivery is fast and don't have to coordinate delivery with UPS/other (which is ALWAYS a problem for me). In comparison, shipping or mailing the entire keyboard I think costs something like $15-$20.

More imporantly, they couldn't simply mail a few keycaps. They told me I MUST re-package the keyboard and accessories as originally shipped, and send in MY entire heavy perfectly good and NEW keyboard (with exception of the few defective keycaps which are super-easy and DESIGNED to be replaced) and they would THEN SEND ME some USED recertified keyboard in its place. I've had more than enough horrible experiences with such RMAs that swap your new for their old.
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EVGA_James
I would suggest getting a complete set of 3rd part keycaps online and just remove the stock ones and put them a side incase you need to RMA.

Well, in this case, then why can't EVGA play the part of this "3rd party" you suggest? If some other company can provide a spare set, then shouldn't EVGA be able to do the same thing? I should be able to...as you suggest...get an entire "set" of Z20 keycaps and put those aside until needed.
That is symantically equivalent to your suggestion, except in this case the actual 2nd party (EVGA) is the same as your 3rd party (which is now also EVGA).
I also suggest ALL keyboard companies should provide a simple process for the customers to order extra/replacement keycaps as needed. It would be superior service. I have needed extra keycaps for multiple keyboards as they wore out.

However, with respect to if I obtained actual non-EVGA "3rd party" keycaps...
I am visually impaired and the EVGA Z20  is the best combination of keycaps/fonts/brightness I've ever seen on backlit keyboards.
There simply is no set of "3rd Party" keyboard keycaps that compares favorably and any such set is therefore unacceptable.

(also...these linear optical switches still appear to be a bit atypical switches so any available 3rd party keycaps out there may not yet even be compatible. The mechanical tolerances are very tight.)
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EVGA_James
But really the keycaps themselves aren't going to break unless you hulk smash them.

It does not take a literally "mangled or broken" keycap to require a replacement. I have used a very large number of keyboards where the keycap character overlays were worn through to the point the characters/icons were no longer readable...and it wasn't just backlit keyboards nor just 1 or 2 keycaps on a given keyboard. It can take less than a year to render some keys unreadable...never mind the aesthetics. And, I've even dropped a tool on one keyboard and badly banged up a few keycaps...so "hulk smash" can still apply to some degree. I even dropped MEK (a plastic solvent) on a keyboard so some keycap characters were literally melted.

And, like my first Z20 opti-linear keyboard, I have had poor quality keyboards where the keycaps caused really severe keyswitch sticking and needed to be fixed or replaced.

Depends on the design and quality of the keycaps.
                                                                                                                                               

Interesting observation.  I haven't changed keycaps that often, but on the one das board that someone had put some white keycaps on, the arrow keys will fly off if I 'flick' the key on the edge like I sometimes do.  I thought it was just this board or keycap, but now know that it is far more common.

The funny thing is that the tolerances inside the switch are far more precise.  If a switch manufacturer can't get the stems consistent, it really speaks to their quality and capability in general.

i had this issue, and i sent it back for RMA because it was pretty unusable, problem was, the RMA one had the same issue just on different keys.
 
I ended dragging it to work and brought it to my laser CMM arm (Hexagon 85 with RS6 laser) to see what if there where any physical differences from key caps. because the RMA process with EVGA right now kinda sucks ass. 
 
Since I don't have access to the solid modules of the EVGA key caps, all I could do was compare them from each other. 
here is what I found :
The switches (Optical Mechanical ones) have .010-.014+ slop in the switch post, with some clearly better than others. They had zero sticking with no keycaps attached.
the backside of the key caps where all over the place, with the offending keycaps having untrimmed flashing and lumpy undersides. These small lumps are only .008 (if that)
using math with lump high spots, they would it would yield around .003 or less clearance, given that the switches have much more movement than these small chunks of plastic. The angle of attack in that you push the down the key will effect if it sticks or not.
(ie if you hit the top of edge of the key with any forward pressure it might cause the key to stick vs downward pressure near the center or bottom edge might cause it work fine)
 
What I believe the issue is the key caps are made poorly in some cheap Chinese injection molding shop, and there are small chips/ dents in the injection molds they are using (possibly using older mold from a older model that uses the same caps to save "costs") I was able to completely fix my sticking keys by hand filing the excess lumps, flashing and "Thick spots" on the back sides of the caps individually so they have the clearance for the switches.