Some cards are not included in the card ease statistics in Anki 2.1.35:
The ease graph currently only includes cards that are currently in the review state. If the cards are in (re)learning, they will not be included.
Then it’s better to add a hint above or below the graph something like that: “Includes cards only in the review state”.
Another point that causes confusion.
If the chart is shown in 10% increments. The pop-up window says “X cards with 150% ease”, but it also includes cards with 155% ease.
It will be clearer if you write a interval instead of a number “X cards with 150%-159% ease”
I do have a similar issue:
I would expect some sort of gaussian distribution to the right side. But for 250% and 270% it shows almost no cards, which is weird at least. Not any show stopper, but it just does not look right.
I think it’s just a combination of the size of the buckets/rounding, and the fact that the bonuses/penalties for hard/easy are 15 percentage points.