Albert Barnes Commentary 1 Chronicles 6:11

"and Azariah begat Amariah, and Amariah begat Ahitub," — 1 Chronicles 6:11 (ASV)

Ahitub - Between Amariah and Hilkiah (1 Chronicles 6:13), this genealogy is certainly defective. It provides only three generations for a period that lasted nearly 200 years, for which the list of the kings of Judah gives nine generations. Furthermore, none of the names in this part of the list appear among the High Priests of that period, several of whom are mentioned in both 2 Chronicles and the books of Kings.

The explanation seems to be that this is not a list of High Priests but the personal genealogy of Jozadak (or Jehozadak), whose line of descent partly coincided with the list of High Priests and partly differed from it. Where the lines coincided, all the names are given; where they differed, some are omitted, probably to make the entire list from Phinehas a multiple of seven. See the note at 1 Chronicles 6:20.