Read by other session - Strange issue

We faced a really strange performance issue in our database today. One report was running for ever. It uses only one SQL and that SQL was completing really fast from TOAD(backend). When we looked at our database monitoring software, we found a new strange wait event "read by other session" was the major culprit.

After rigorous googling we decided to flush the shared pool.

alter system flush shared_pool;

It took really long time to flush the shared pool. But after clearing the shared pool the report started completing really fast.