Items and mobs vanishing/despawning at random from chests and confined areas

My friends and I are on a realms server together, 6 people total. We have started to notice some items disappearing at random and have been chatting to make sure accidental theft is not involved, but can confirm items are disappearing at random. There are a lot of items in inventory between us and we all play with different frequencies, so it is possible other things have gone missing we haven't noticed yet. That said, here are the first things we've noticed:

I went exploring outside our player village and found several treasure chests both in sunken ships and from buried treasure maps, including 4 or 5 diamonds. I built two waystations for myself to make return to these areas easier and established a single chest in either place. Returned home with my full inventory and unloaded into my private chests in my house. Played for another half hour or so, then logged out. Loaded back in a few IRL days later, but found the diamonds missing from my inventory. Asked other players, but none of them even knew I had diamonds and no one had more diamonds than before or unexpected diamond items. Figured I'd must have forgotten and left them in one of the waystation chests and went back to check, but no dice. Never found 'em again.

Another player had previously captured two axolotls and named them with nametags. She made a pool for them by her house, with a waterfall, and they were there for several in-game days with no issue. I was the only player on the server for several more in-game days and the chunk was loaded, but I never went to her area and did not see the axolotls. She came back about a week later IRL when I was not there and the axolotls were gone. I felt really bad because it was probably on my watch, but we'd never seen any issues with them or the enclosure and as named pets, they shouldn't have just despawned. Genuinely tragic that we lost them, and now I'm watching all my pets like a hawk every time I'm in-game.

I was playing again about a week later IRL and made a chest just for maps, which I filled with stuff for compasses - iron ingots and redstone, plus paper. Didn't open the chest for several in-game days, and when I did, two stacks of iron ingots (four pieces each) were completely gone. And not in order. One was from the second inventory slot and the other was from the 8th or 9th slot (I had several stacks of four next to each other). No one was on with me, so they could not have been stolen between me placing them and them being gone when I re-opened the chest.

Just today, a player who hasn't been on very often jumped back in and remarked that their diamonds from the public chests in the town square were missing. I sorted those chests about a month ago IRL and recall seeing the diamonds and sorting them, but I did not take them and none of the other players recall even seeing them. They're completely gone from the chest and again, no one has any unusual or new diamond items or extra diamonds in their inventory.

Again, it's possible other things have gone missing we haven't noticed. It was a couple weeks IRL before I could check my waystation chests again and I don't remember what I left in there. Another player has enclosures for chickens, sheep, and cows and it would be hard to see if any of them went missing. Some of us have barely played an hour in the last month and some of us have been on every other day, but we keep to ourselves and don't borrow from or share inventories outside each household. I've seen posts on several forums of similar issues with weapons and armor as well and everyone always assumes player theft, but we are close friends and trust each other and can confirm through other disappearances and player presence in the game that things are definitely disappearing and not just being stolen. We're not really sure what to do here, but it's really frustrating that we're mostly losing high-value items and pets we can't replace.