The problem is with items with the EntityTag nbt tag such as below. [minecraft:give @s minecraft:armor_stand\{EntityTag:{Small:1b}} 1] Placing the armor_stand item in single player will place a small armor_stand, and that happens sometimes on a spigot server with no plugins. However as soon as the item updates, the item breaks and looses the EntityTag nbt tag. This causes it to place a normal armor_stand. Things that cause the item to update and therefor break are: Clicking the item in your inventory with any mouse button, moving the item in your inventory, hovering over the item in the inventory, and sometimes just opening your inventory causes the item to break. When an item breaks it also breaks all other items like it within the same players inventory, regardless of whether or not that item was updated.

We have thoroughly tested this on spigot 1.14-1.14.2 and it breaks on all of them, does not break in vanilla, and have tested plugins. Nothing is breaking the NBT data other than something within spigot itself.