There may be a problem with the ratio of quest items on the portal.  I have been on it for weeks, doing every quest (though I am sure I missed a couple of them) and I have gotten a huge number of ancient horns in comparison with the other quest items.  I have managed to get 4+ money trees, 4+ snake eyes, significantly more than 4 ancient horns, and numerous blueprints for buildings that use these items, but I have not gotten a single nightcat or spirit in a jar.  Seriously, my pets have managed to gain something like 20 levels here and I'm going to assume that they will all be level 50 before a single spirit ever appears.  Could you maybe create some sort of trader NPC who can let us trade 1:1 for any quest items from the portal?  That would let us stay long enough to get what we need and then move on.  I have given away or sold dozens of throdamas and symurghs during my time on the portal; I just need 4 spirits and I can leave.  Judging by the state of the item trades, I'm not the only one who never gets spirits to drop.

The probabilities for all portal items by type are equal, blueprints have 4 times less probabilities than materials. Every item has the same probability to appear on every portal trade, and these probabilities still remain the same and not lowered when an item of a certain type was traded on the previous cycle. For example, getting 5 Ancient Horns in a row doesn't affect the probability of getting another item on the next cycle.

In statistics theory, usually a very large number of iterations is needed for a reliable selection that represents the formula that stands behind the numbers. It would be impossible for a normal user to see the accurate ratio between the portal items. There are no bugs here, just bad luck.