Parallel queries waiting on a session in WAIT EVENT "PGA memory operation"

Does this sound familiar to anyone?

Problem Description

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When running a query with in PARALLEL, on occasion,

- a bunch of Slaves are created

- most of them are waiting on "cursor: pin S wait on X" events. The Final Blocking session for all of these sessions points to a session with an event of "PGA Memory Operation"

- The Session waiting on PGA Memory Operation keeps changing

- The PGA Memory Operation is holding locks for minutes in some cases

- Queries that run in seconds are taking 5-10 minutes

- When the same query is ran in multiple sessions, they all get backed up