This issue has been a while and I did not notice anyone mentioned that.
It appears AH's average price sorting is not done properly or it is done with a whole number only.
e.g. for the price of a stack of 99 gem stone, the sorted price can be:
5717, 5717, 5717, 5707, 5717, 5717, 5707, ....
I suspect it is sorted by the whole number of the average price.
The average price of 5717/99 = 57.74
The average price of 5707/99 = 57.64
The whole number of both is 57 or both have the same round up number 58.
When there are many in the same whole number in the listing, the lowest price can be in the 2nd or 3rd page.