I think you guys missed that I questioned that recipes are uniformly random. In this context meaning that every distinct recipe has the same chance of occurring. They may still be random, but e.g. UUU may have smaller chance of occurring than some other recipes. And that chance may vary other time, and/or per player.
No one that I know of ran accurate records of all recipes showing up over meaningful period of time, and that's how you can determine statistical properties. But I know that with with consistent usage (3x times a week, occasional brown bear feedings recently) my Pet Food stockpile has been changing consistently since PF introduction. I.e. in this case my stockpile grows ever so slightly week over week. There are some ups and downs, but over monthly timeframes this is very consistent.
Now, I also try to use UUU consistently. And until about Phoenix Event I was able to field 1x UUU every tournament, and my stockpiles were essentially flat. This was consistent with uniform frequencies hypothesis meaning that on average every recipe shows about once per week. Again, very consistent stockpiling at least on a monthly basis. But then in subsequent months I ran out of my 7-8 stored UUUs very quickly, and was able to field 1x UUU in only about 3-4 tournaments per 9 week cycle. This, again, allowed to keep my stockpile of UUU flat (and stockpile was really 2-3 units). Again, this pattern was very consistent for about 6 months.
And then about a month or so ago (around start of Elvenar chapter) things changed again. UUU are a lot more frequent now. I mean, A LOT. I have 10x UUUs from Elvenar chapter, so that's last 30 days or so. This includes one day when I got 2x UUU in a row. Even in the better days 10x UUU would be about 10 weeks worth of waiting. In not so good times - about 20+ weeks. Now it was done in about 4.
Could it be explained simply by chance? Sure, just about anything can be. This is also a pretty unlikely scenario if we assume uniform distribution. I wouldn't be expecting seeing such variations over long periods of time.