Performance issue in Postgresql 12

It is a Java and Hibernate based application that processes rows in a table. The application when launched loops through rows in a table, executes anywhere from 10-25 queries per row and inserts results into two other tables (one mater record, and a bunch of detail records).

The processing speed is about 370 rows per minute in the first 30 mins or so. After that, it slows down significantly to barely 14 rows per minute. I am trying to pinpoint the issue whether it is database or application or OS related.

Any thoughts?

Thanks in advance.