So I noticed a bug with collection quests in general: after you finish them, the items you collected would still stay in your quest inventory. This would cause your quest inventory to full, and any other collection quest would not work because your quest inventory was full.
A quick fix to this is simply discard old items out of your quest inventory. To do this, press J and click on old items in your inventory. drag them to the trash bin in your inventory window and voila! Collection quests should work again.