It's like a "Negative Confirmation Bias", or seems that way to me.

The idea that drop rates are different for different groups is the single biggest problem with what's being reported.  It makes no sense from a programing or a business perspective.  Why would they spend money to go to the trouble of singling out a "random" group of players?  I believe it is possible, but it's extremely unlikely.  Extreme hypothesis require extreme evidence.  And this study is only anecdotal.  There is no statistical comparison to a well stated null hypothesis.

Is it possible? Yes.  Is it likely? No.  Is there evidence to support it?  Only limited anectodal evidence.  There may be enough for someone to spend time looking into further, but at this point there are several equally if not more plausable explainations.  Bad luck, bad sampling, etc.

I could use my results above to claim that drips for legendary books the first half of November were 'modified' using the same argument that it applied only to me and not everyone.

I think you proved that nothing is going on here other than a biased sample.

You state that some are having good drops, then reporting numbers of the not so "random" subset that is being targeted for worse drops...

Do you think it's a bias to see such a drop for three weeks? Nothing but books falls 

This single 41 second video isn't bias, it's not even a sample. It's the loot chests a single person opened on a single day.

And the fact that such chests have been falling for three weeks does not mean anything to you? Or do you think that I am deceiving you and I have nothing else to do but write about it here

Self reported data is extremely problematic. Not only do we get only negative reports, those people can report whatever they want. 

Let's say someone has a string of 30 chests they opened, going back from today, that have not dropped a legendary book or sacred shard. They go on reddit to complain about their luck, or some other social site, and see someone else has had bad luck, and is posting about only epic books and talking about how CB rewards have changed. Now it's a pattern, nevermind that 500,000 or 1 million people haven't had any complaints.

What's worse is, that person says they haven't gotten anything but epic books and ancient shards since November 16th. So now, even though you have only had 15 total days without a sacred or legendary book, it seems like it is the same problem, that you haven't gotten anything in the same time frame. So when you go to report it, you also report it as November 16th since you got a sacred.

People also purposely misreport to "make people aware" of a percieved issue, making it look worse than it is to garner attention and action.

There are regular problems we face in research all the time.

Do you have any idea how many chest are opened with NO books AND NO shards?  If anything this is good luck, just not the luck you want most.

It's not luck to see some books for three weeks, it's a pattern

Luck is random.  Random is a pattern.  As opposed to uniform patterns and clumped patterns.  You don't even have to take a statistics course to know this. It's taught as a 1 week lab in a majority of upper level science courses when you're learning about t-tests and chi-squared tests.

Three weeks, or what I assume to be 42 chests of top nightmare is a woefully small sample size for data. 

For example, your projected values during that period:

2.56 sacreds

8.96 ancients

1.28 voids

4 epic books

2.65 legendary books

Given the low odds of the resources we're looking for, it is very, very, very (cannot stress this enough) easy to have wildly different results over months of clan boss chests, let alone three weeks. It doesn't mean that the clan boss drops have changed, nor does it mean that there's a pattern that proves anything other than the fact you were unlucky.

I'm trying to tell you that for a year there was a normal drop with the boss clan! There were legendary books and sacred fragments and water fragments, and then, for no reason at all, it began to fall asleep with epic books! Do you understand that? There is nothing but epic books, nothing at all! Don't you think it's suspicious?and I'm not the only one who has such a problem!

Negative bias/reinforcement would be when the likelihood of an event occurring/being reported goes down as a consequence of the action occurring. Positive would be when it goes up. In this case, the more people report the problem, the more likely it is that people will report the problem.

You are using a priori logic.  You draw an erroneous conclusion that "for no reasan at all."  And you draw the conclusion that rates must have changed, and only for certain accounts.  When there are obviously other possible explainations.  And this data provides ZERO statistical tests to demonstrate your conclusion.  All of our statistics are descriptives; not tests, not comparisons, not rigourous research in the least.

Even if the tests were performed, there'd be problems with sampling and sample size.  Not to mention reproducability.  Can you reprodcue these results in other samples?  Can you reproduce them a month from now?  Two months from now.

I do not dismiss your observations.  But that's all they are.

Yes I know. I put quotes around it for a reason, rather than just saying Confirmation Bias or Positive Confirmation bias. But thank you for making sure. :D

This is one of those topics in class I have fond you must break down. How is negative things happening to me a positive bias? is a recurring sentiment.

During September and October, I accumulated 20 legendary fragments from 40 purple and 150 ancient and 37 legendary books, and now one epic book falls to me every day for three weeks! it doesn't look like a failure! It's not like that at all

Sounds like you had a great run! So much better than my September and October. 0_0

Alright, so let's make the assumption that September/October were 60 days of 2x chests from NM/UNM and that you're reporting correctly.

Expected value from 120 UNM top chests:

19 epic books

12.7 lego books

60 ancients

21.8 voids

16 sacreds

Expect value from 120 NM top chests:

11.3 epic books

7.584 lego books 

25 ancients

3.6 void

7.32 sacred

Grand total expectation of: 

30 epic books

21 lego books

85 ancients

25 voids

23 sacreds

So during that time span you ran a little bad on sacreds, insane on ancients and voids and absurd on legendary books. Then you were unlucky the past three weeks. Riveting stuff. 

Also:

https://en.wikipedia.org/wiki/Variance

and then you want to tell me that I was bombarded from head to toe with epic books and nothing else is just a failure? I doubt it very much!

I would very much like some epics. Please share.I am totally out and have like 10 epic champs I need to book for Hydra.

Also, remember, that while I totally disagree that you are being affected by any bugs at all, that I DID report your thread here and your numbers, to Plarium.