I'll try breaking in the switches with a large book or something, but the space bar just won't do.
Here is a video showing the difference.
feature=youtu.be
I just checked my Ducky fire 69 which has a blue MX spacebar and while there is a small amount of rattle, it doesn't sound anywhere near as bad as yours. It does sound like your stabilizers are loose or something or a different stabilizer is being used, so it's really hard to tell, The main problem is that the Fire 69 uses black stabilizers while the Shine 5 uses red stabilizers. I don't know if there is a difference besides the color or not. That being said, I just compared my regular shine 4 (MX brown) space bar with my Year of the Goat (MX brown RGB) spacebar, and even after removing the O ring from the spacebar (or maybe I lost it cuz it wasn't on there when I removed it) from the Shine 4, I can say that the Year of the Goat seems to have slightly more travel distance (this seems to apply to the letter keys too though), and the space bar movement seems "crisper" on the Year of the Goat (if that makes sense) even though the tactile bump seems slightly less pronounced on the YOTG. Maybe "crisper" means 'more bouncy' since there is somehow more travel distance on the YOTG, but whatever.
As far as the space bar issue you have, I can make my Shine 69 'rattle' but nowhere as much as yours does. The rattle on my MX blue spacebar is definitely far louder than on the MX Brown, but it's 100% normal and expected on a MX blue spacebar. I did check my *second* shine 69 (Yes I have two) and that spacebar does rattle more than the first, but then again that board has a lot less use on it so it isn't broken in like the first one (the first one is my 24/7 daily driver).
Yours does seem excessive, though.
However I will say this.
About the travel distance with the "MX Browns" from the shine 4 to the Shine 5 RGB, the travel distance I am talking about is from button fully released to the tactile bump. There seems to be more distance from full release to the bump/actuation on the Shine 5 than on the Shine 4.
That COULD easily account for more "ratting" on MX blue RGBs if there is also more travel distance from idle to the switch mechanism. Keep that in mind for what it's worth.
I would take off the spacebar and check the stabilizer and make sure that it's properly mounted. Then just use it for a week.
And edit: I just removed my fire 69 spacebar and noticed that the black 'square' bracket that the black + stabilizer sits in also wiggles but moves around less than 1 millimeter, but it does wiggle and isn't 100% stationary. That wiggle has absolutely no effect on rattle, though. In the Shine 4 MX Brown, it -also- wiggles but wiggles even less.
I did grab the black + in the shine 69 MX blue and move it upwards out of the black square bracket and there is a lot of play, as expected (the same in the shine 4 mx brown).
It's really hard to tell, but we need someone else with a Shine 5 MX blue to post here with their space bar findings. I'll post on reddit and see if someone can reply there, but the rattle COULD definitely be caused by the increased travel distance from idle to actuation that I notice on the shine 4 mx browns.
Does your stab seem normal if you grab the + and manually move it up and down with your fingernails?
Put the spacebar on then make sure you press down hard on both sides and then play with it.
*Edit* again.
Just checked my Year of the Goat MX Brown space bar.
While the overall sound is about the same as on the Shine 4 Brown, it *definitely* rattles more, noticeably so. Not a problem to me but it's definitely nowhere nearly as "tight" as the Shine 4 one is. I'll post on reddit but seeing that, I can see how the MX RGB blue spacebar can be that loose on yours but I'll ask the others.