As  frustrating as it might be, and expensive, it is not guaranteed that you will get the items. 

It only says what you might get. 

According to the information about the other UBERS, you are fishing in the wrong pond for Total offence  gem TAAFFEITE  you need the AVARIN invader.  

I tried posting the link , but it couldn't be seen very well, and it also didn't appear to work.

GHALL3

You may have just been very lucky when  you got 4 Legendary  gems from 6 Ubers, and very unlucky the rest.  

Luck isnt the same as chance.Chance is fixed,with luck you can beat the odds.

There are 8 gems mentioned, so if these were in a bag every time you took a gem out, there is a 1/8 chance of getting a specific one.

You put the gem back in the bag,(you are not allowed to leave it out) and try again, it is still a 1/8 chance.You could try 6 more times and still not get the one you want.

Now supposing instead of there being only 8 different gems,they add a few more items to the bag.

Ubers drop things apart from gems.

For simplicity.

Supposing they add one of each other gem, but none of Indicolite,the odds of getting this gem now drops to1/15.

Unfortunately, we dont know what the % chance of getting a particular item is,they dont publish the information, nor when and if it changes,or if its been adversely affected by a bug after an update to the game .

I notice the first event was KvK  the second time was CvC, how long after was this,and the other times you are complaining about,were they comparable conditions ?

It isn't as simple as a 1 in some number chance at getting the unique gems. Let's take into account that you have 20 invader items which have a chance to drop and each of those have 6 levels (simple to legendary). You also have 8 gems which have 6 levels. Now you need to add into this bag the fact that each of the simple resources can drop (diamond, glass, etc) with those also having 6 levels. Plus the varied speed-ups and boosts that can drop from an invader. So let's just grab a random number and guess that maybe there are around 1200 individual items of varied levels or time ranges in this bag.

However, they truly aren't all in the same bag. They may very well be in 100 different bags; separated out by low level bags up to the most unique and desired bags. When you hit the invader, the things which might be calculated into the bag which you get to select from could include how much damage you do, how much damage is already done to the invader, what percentage hit bonus you are up to, the level of your hero or shaman etc etc, plus the good ole fashion random number generator.

If you score a low number then you get to pick from the low level bags. The higher number you roll then the higher level the bag is. Even if you get a high level bag, you then have the random calculation generated for the item you get to pull from that higher level bag. So, you might get fortunate and eventually get to pull from the unique gem bag, but ultimately still only get a simple or usual gem.

Basically, what it boils down to is build your hunting gear, do your invader research, level your hero and upgrade the invader skill section, then kill kill kill and then kill some more. Most importantly, just enjoy the game. 

You have responded quite a long time after the topic was first raised here.

Ideally the topic should not have been posted here, but in one of the other sections of the forum. 

My explanation was to try and keep things simple,as I appreciate that programming is much more complicated and that what item or items is determined by path ways, as you described ,but where there are probably only the options of  1 and 0, but there may be many of this options occurring before the decision of what you get get is made.

I cant argue with the fact that the more you do to develop your hero and reduce energy use the better things should be.. 

However, as I haven't  hit that many Ubers at all, or even recently,  I do not know what, or if, any thing has changed about what exactly you can get from attacking them, though I have read that you don't get common materials from them, and keys are now also  found, but I cant confirm either of those suggestions.

I would think most have.

Yes the jackpots are rare otherwise they would make little profit, and of course the same thing applies here, except, though you don't have to take part in either of them,if you play the game and want access  to everything in it, you are forced to attack invaders and Uber invaders.

So would hope for more reasonable returns.