Several villagers and items despawn

Ca. two months ago, I started to build  bases for my villagers (for example smithery) so I can buy a full diamond armour and all diamond tools and weapons. But two weeks later my first villager despawned: my toolsmith, who traded diamond hoe, shovel and pick axe. I was very disappointed but I made one more time a toolsmith but he only trades a stone hoe. I built again at my villager bases. I was almost done but then my second villager despawned: one of my two armour smiths, who traded diamond leggings and helmet. One more time I was very upset and I thought about writing feedback to you. But the problem seemed not to be that big for me and I made one more time a new villager for my smithery and named my most important villagers. My smithery exit is secured by two doubled oak fence gates so there is a small space between outside and inside the smithery, so to speak a small lock. The villagers surely can't escape. Since I gave them some names they didn't despawn, but today I went to my nether fortress and collect some wither skeleton skulls to fight the wither and get a beacon. Then I come back with the skulls in my shulkerbox. I place it down to get room in my inventory for the fish, which I catch to repair my elytra. I collect the shulkerbox again and go to fight the wither but then: my Minecraft crashed. I went again in my world but my shulkerbox is no longer in my inventory. I look at the place, where I put it down but it wasn't there too. I really don't like to collect more skulls and in my shulkerbox there was some potions too, so now I write you!

I hope you can support me,

Yours,

TynookMinecraft

PS: There is my smithery (screenshots) and 2 minutes ago, when I did the screenshots I saw: another armour smith is despawned= names are not the soloution