Unknown injury that lead to death

So yesterday I had to put two of my 5week old meat kits out of their misery. I'm not sure how they did it, but at totally different times during the day the two kits had injured their necks. They didn't feel broken, but the kits barely moved their limbs and would kinda oddly turn their heads. I know they are injuries because I heard them screaming when they happened. One I buried because I couldn't process it before the meat would have been iffy to feed my dogs, but the other one I did process (also my very first processing!!!), and her organs we're all healthy, but her spine in her neck was curved like she had dislodged it out of place. Has anyone else have this happen, and possibly know what happened/how I could prevent it in the future? Also after I gutted her I found a pocket of air behind one of the front legs. I didn't notice it up to that point, so could I have caused it while processing her?

It's possible that they were startled by something and ran into the cage wall hard enough to hurt themselves. I've not experienced it personally but I've heard rabbits can break their necks that way.

What time of the day was it?

One was at 5am, and the other around 1pm.

i had a similar issue with a kit that was actually around the same age, now that i'm thinking of it. there were three, two were lost to what i'm assuming was heat stroke, so brought the last one inside. a couple nights later we woke up at 3am to her screaming and unable to stand. i euthanized her, but when i skinned her out, i couldn't find anything wrong (though i used cervical dislocation so any neck issue was destroyed i guess.) i never found out what the issue was. i guess i'm just saying this to say you aren't the only one hah

i can say though that the pocket of air behind the arms is normal i don't know why it's there, but it's always been weird to me haha.

what kind of feeder do you use? maybe they were too eager to explore and got their head stuck and when trying to free themselves they got hurt... that's just a theory....

Neck and spine injuries can happen with nothing to get injured on and should usually be investigated for possible predatory threats bothering them or new things that they may be overreacting to. With younger ones though that could be quite minor things that aren't actually a threat. Spooked rabbits have strong enough legs to smash into objects harder than their own bones can take. Heavy or attached cage items would make that easier to do and covering the sides or placing them in corners or between other cages may make the sides more obvious to avoid along with less things to spook about but the "bunny blender" effect with deadly accidents can happen even in large, solid walled colonies. When you get several young rabbits dashing around an area eventually someone makes a mistake about a wall or object. I've seen them do it in 12' colonies as easily as wire growout cages. Sometimes you can have a single one spook in a straight line into a wall but usually those have more limited experience with small spaces or an extra nervous temperament anyway. It's one reason trying to cage wild species doesn't go so well. They will inevitably smash into their new contained space a few times. As they mature, experience more things so there are less scary surprises, and get bigger relative to their surrounding space they are less likely to attempt bolting and more likely to remember that they will hit something. Around weaning age puts together the variables to most likely try to run from something without paying attention to space.

Not that you can rule out just stupidity with objects such as sticking their heads and feet in gaps they shouldn't on the cage, feeders, or anything else in the cage. I've dislodged a variety of young animals from J-feeders and not always the obvious simple shape of the J-feeder but the various designs for lids, cage attachment, and how tightly the edges meet or the corners are finished. Don't use J-feeders with chinchillas.... They will do things rabbits can't even think about accomplishing.