A scribal error.
The is-i is omitted by a through a simple scribal error.
The Hebrew text of the book of Ezekiel is not in good condition - it is full of scribal inaccuracies and additions.
It is, however, characterized throughout (except in some scribal additions) by a definite thought, and pervaded by a definite tone of feeling.
The reading of " 9 soss and 36 years," which gives the total 576 years, he suggested was a scribal error for " 6 soss and 39 years "; he thus reduced the length of Dynasty III.