Just adding my same experience: 500 loads, 400 runs, 300 Chiltara kills, Zero GG.
I have tried with the Season dragon pet and without, with other pets, solo run and with others, on two difference characters, I have killed every mob before Chiltara, No mobkills before Chiltara, I have tried with different spells/skills, I have opened chests and NOT opened chests and NOTHING YET.
Have you tried the most common piece of advice: Lower the difficulty?
The theory is that as you have more magic find in the game, you have a higher chance to get more items in general, and when you do get an item, it is more likely to be a higher quality drop, so they might be competing with a non-magic-tier item, the Gibbering Gemstone.
Also tried the other suggested thing, farming in the Campaign Mode? Chiltara is a guaranteed spawn in the Caverns of Frost in Campaign Mode, however in Adventure Mode it’s not. By farming in Campaign Mode you can eliminate one layer of RNG.
The Diablo RNG Gods are older than Heaven and Hell, and the arguments of bugs vs bad luck vs broken vs developer vendetta are just as old, going back since Diablo 1. In Diablo 3, at least you have a much better chance for getting all items, you really are.
Players today expect being able to achieve everything and obtain every item in games with minimal effort and time.
In some games, you might never get a certain item because it’s that rare and hard to get, but Diablo 3 is NOT one of those games.
Same here my friend, I’m very disappointed that they didn’t care about this problem.
Did the staff in all three regions.
First Europe. 10 runs, no luck. Created a new char and ran campaign until the Chiltara part. She dropped the stone with the first try.
Then US. Tried it in campaign mode directly. Restarted the Chiltara campaign part 4 more times and had the stone with the 5th try.
Then Asia. Got it on the first bounty that had the Frost Caverns.
OK, might have taken me gazillions of runs on EU server (too), but gave the campaign mode a chance, because RNG is a b… and the you die… 
And it worked out extremely well. That I got it on the Asia server with the first “correct” bounty, well that was definitely pure luck. Too make the résumé short, and of course this is only my subjective experience:
It falls way quicker in campaign mode.
Maybe I should play the lottery…
For sure you should play the lottery, I’m printing everytime that is doesn’t drop, must be 50 prints at now, without counting the 100 times trying… Tried every way, every difficulty, campaign, adventure mode, with others, and nothing yet here, chiltara hates me.
Just fix it, raise it, we are limited in this game cause of it, maybe I’ll have to go in law because of poor customer care?
That would be a hilarious consultation to have your lawyer sit you down and explain how the world works to you.
You to your lawyer: I want to sue a video game company because they made an item in their game too rare. I think they should have to pay me lots of money.
Your lawyer: What are your damages?
You: Mental trauma from looking for an item in a video game.
Your lawyer: What is their liability? What legal obligation to you did they violate?
You: …
Your lawyer: Typically, you can sue for your damages multiplied by their liability, and since you have no damages and they have no liability, you can sue for $0 x 0 which is $0.
I got it on my 10th time, in campaign mode. I was also in a group too with 3 of my friends. So maybe get friends if you have any and do that next time maybe it will drop sooner.
In Brazil actually you don’t need a lawyer, there’s a competent body that oversees consumer rights, called by procon
And in particular, it would be for them to fix this altar of rites with this request that has been impossible for many to carry out, proposing only a fine if the company does not collaborate in resolving the abusive practice of a impossible drop, which one it has been for too many people, as you can see in forums
There is nothing to fix - multitudes of players who have carried out the request make this claim invalid.
Again, multitudes of players have received this ‘impossible’ drop.
Not sure how law works in Brazil but according to US laws, where Blizzard is headquartered, your case has no merit. You have not suffered any financial, physical, professional or emotional distress for not completing a task in a video game. Your claim would be laughed out of court.
What “consumer rights”?
When you bought D3, you bought a license to play the game. Your “rights” do not include guaranteed completion of all Quests, Bounties, Season Journey Objectives, Seasonal Conquests or Seasonal Theme Objectives.
You currently have 4 Level 70 Seasonal Characters with 2,705 Paragon Points on the Americas Region. Are you telling us that you still have not acquired one single Gibbering Gemstone?
I am not a skilled gamer. And even I have crafted 6 Staves of Herding this Season.
And I don’t even have half the Paragon Points you have.
No, my friend. As others have tried to tell you: I don’t think you have a solid legal case. Maybe you should stop running Rifts and start farming back-to-back Caverns of Frost.
Let us know how that turns out. I would love to hear what your consumer rights procon would have to say about it. I am sure they are not working on more important things.
If Blizzard is causing you harm by forcing you to waste your time on a rare drop, you can just stop playing the game in order to mitigate your damages.
By your logic, you might as well sue the country for not winning the lottery. At least that way you can show real mental trauma, as well as financial losses from buying a bunch of lottery tickets and not winning the jackpot.
I swear, some people have zero grasp on reality.
I am on like 35 kills of Chiltara without dropping the gemstone. I had about an 84% chance of having the gem by now, but I did get other mats quite easily, especially the liquid rainbow, which I got two of on two visits to the cave on separate occasions. I also found the black mushroom just through normal campaign progression, with only one visit to the spot. Win some lose some I guess.
But still, 250 kills without gemstone? That’s blizzard’s fault.
For someone to have the gemstone drop on the first try there must be someone to have 250 “empty” kills. 
That’s just stats, bro. It’s nobody’s fault.
It’s the designer’s fault for making the drop chance so low and not putting in a pity counter thereby enabling the possibility of 250 kills and zero drops.
I would say that the drop rate is fine since it was originally intended to be an easter egg item only.
The problem arose when they made it a requirement for the Altar. They should not have chosen the Staff of Herding as a replacement for the Set Dungeon pages, and instead chosen something else.