This happened to me and my friend (we play in the same world) three times already. We fly in our world and die due to kinetic energy. When we get to the place where we died all our stuff is there except the Armor we wore and our elytra. First, I thought that is was just very close and the rest of the stuff was about to despawn but now it happened again and it was just a very short trip but still no Armor and elytra.

I play on a Predator gaming Laptop and my friend uses a custom build PC