Minecraft 1.14.4 villager won't collect 8 seed packs
Solution 1:
Villagers currently can hold only 4 stacks of items of one kind. You can fill the remaining 4 slots of the villager's inventory with wheat, or leave them empty so the villager will fill them with picked wheat on his own. As long as there are no other plantable items (seeds/potatoes/carrots) within the villager's reach, the remaining space is not a problem; it may delay the time the farm starts "operating at full capacity" but won't prevent it from working.