Items Disappearing

But if the zombie had it and then despawned?

He would have put on the armor, visibly, and had at least one of my items in his hand. None of these happened.
The items vanished / despawned.

Can enraged mobs ever wear armour?

In my instance I was with two other people fighting Momentus.
We set our spawn at a bed nearby...
I died but came back to my death point not a minute later, where I couldn't find my items and neither did my two friends ever .__.

I lost some of my items from falling, although someone may have taken the good stuff, because I got back the junk. I don't know, though.

I don't believe so. Mobs have a pick up loot tag, and I think that's off.

The last non-mob death I suffered was a boating glitch (that 100k journal thing), and BigDavie found and recovered my items just fine.

That sucks. I was in the nether yesterday and a pack of nether hounds killed me. Luckily I got my stuff back... but for your problem, maybe the zombies picked up your stuff? I don't know, but I think zombies can pick up swords and armor and wear them. Panda lost her head from dieing by a zombie, and the zombie was wearing her head, it looked freaky, but it could be it.

I don't have problems when battling enraged zombies, when I do die I can recover my stuff. I never had that problem before. I did lose all my stuff to Momentus, but I didn't want to get to close to him to get my stuff back. Though one time, I died by a zombie, and I dropped a head, and then the zombie put my head on. It was weird.

I'm aware that it's possible for mobs to pick up and equip player items. I've seen regular zombies holding their own rotten flesh on occasion.
If the items aren't "coded" to despawn instantly, the only theory that makes sense would be these enraged zombies attempting to pick up items, having it somehow "removed" from them (or being otherwise unable to equip / use the item they take) and then picking up a new item - depending on how fast the process is, it could be they "vacuum up" all the dropped items in an instant and those items are removed from the zombie's clutches. In which case, being able to equip and use player equipment would actually be a good thing since at least the Enraged zombie could then be killed (in theory) and all stolen items reclaimed.

Actually, enraged zombies are completely different from just the regular zombie. The fact of vacuuming up all the stuff is a possibility. But, I have yet another story of me and Panda to share. We were in a mine, mining, and all of a sudden this enraged zombie comes out of no where and takes out the both of us. We luckily got back into the mine, and the stuff was still there. I don't think it vacuums up the stuff because of that. Next, Panda sacrificed herself for the enraged zombie so I can get the stuff, and all went well. The zombie was defeated, and it was a happy ending, (with no diamonds). Okay, so I don't think that the vacuuming part is real, but since there was a lot of enraged zombies, they could've each picked up an item.

i got lucky when i died because i feel in a whole with 2 of them, they had despawned by the time i got back to the spot and all i lost was steak

Then I have no idea what the hell is going on. All I know for certain is I have died to enraged zombies on three separate occasions and everything I own has vanished. Whether the zombies are doing it, the game, or something else entirely, I have no idea.

Actually one time I was fighting momentus and only had stone swords And every time I went back after I died it seemed like I lost most of the swords I crafted over 20 and going back multiple times to the same spot only got like 8

It's sad to here that your stuff is gone. It could be some stupid glitch for all we know. But I hope you can replace your stuff.

I can, just takes time and a considerable amount of grinding.
What gets under my skin I guess, is that I never had this problem before enraged mobs, and all this latest incident has done is reinforce my utter hatred for them. Unfortunately, while I can point and say all three times it's happened has involved enraged zombies, I have no way to prove that they are in some way bugged or causing the glitch. I'll believe there's nothing (intentional) in the code that's set to destroy items, as that would be silly. But while I've never been afraid of the wild before, at least then I knew if I did die I had a reasonable chance of recovering my things. Now... hell, now I don't even want to set foot outside of town unless it's broad daylight.

I go MH a lot to get mob drops. I don't see a lot of enraged zombies or skeletons, but sometimes I do. They are mostly under ground in the mines, because every mining expedition that me and Panda go on, we at least stumble upon enraged zombies. It's harsh, because if we aren't wearing any armor, they do hits that take away half of the health bar. It's more dangerous with enrages zombies. Surprisingly, the first time I ever saw an enraged zombie, I was coming to help Panda who was stuck in the wastelands. I was up on a mountain cliff, no weapons, and amazingly killed it with my bare hands. That's a once in a lifetime thing to do! Now, I know these things are wickedly fast, and strong. This only means all of us need to be careful in the wild. (Though, any wild trip it better than nether trips)

Probably. But I don't know about my mining trip with Panda. Cause it at least took us a few minutes to get to the spot we were mining it. The nether hounds actually seem like enraged mobs. They catch on fire, and have bubbles around them with great speed. Anyway, I was killed by a pack of them, and it took me at least 10 minutes to get to my stuff, cause I had to go through a nether castle filled with withers and blazes, and then when I got to my stuff, the hounds were still around it. But luckily I finally ran to my stuff and hid under nether rack. I hate nether trips...

Since you were AFK, your death screen could have been up for longer than five minutes, and I believe the death screen keeps a chunk loaded.