John Gill Commentary Ezra 2:62

"These sought their register [among] those that were reckoned by genealogy, but they were not found: therefore were they deemed polluted and put from the priesthood." — Ezra 2:62 (ASV)

These sought their register among those that were reckoned by
genealogy
To find their names written and registered there; for the Jews kept public registers of their priests, their descent, marriages, and offspring, that it might be known who were fit, and who not, to officiate as such:

but they were not found ;
their names were not there, nor any account taken of them:

therefore were they, as polluted, put from the priesthood ;
were not suffered to attend at the altar, and offer sacrifice, and enjoy the privileges belonging to that office.