Playing in Realms (both my own and others) sometimes when mining blocks or collecting items dropped in the world, the item is collected by the player (i.e. it disappears from the world) but never appears in the inventory.

If I disconnect and reconnect, the item remains gone, so it doesn't seem likely to be an error collecting the item, but rather an error allocating the item in the player's inventory.

This may be related to why some items are replacing other items in the player's inventory.