This is odd, but i've tested this with my server and single player. Happens on both.

When you have a LootTable spawn another LootTable. It will make anything you have inside only set 1 item. Regardless of what you have set for the count.

Here is a datapack to test this with. 

Do /loot give @a loot ghostly:chests/test     You will only ever get 1 egg.

But if you do the base loottable with

/loot give @a loot ghostly:chests/blank       It will work correctly giving a random number between 1 and 6 eggs.