PLAN_TABLE row lock contention

In a third party application, comprised of several processes accessing our Oracle database, we see process threads stuck waiting to acquire an Oracle PLAN_TABLE row lock. All are waiting to lock the same row. Meanwhile another process within the application holds a TX lock on that row for hours and hours. This PLAN_TABLE is in the application user schema, whereas PLAN_TABLE in the SYSTEM schema seems to be quite unused. SQL tracing must be enabled with DBMS_SESSION.SET_SQL_TRACE() or the equivalent within the application itself. If manually initiated, it would not persist across restarts (I believe), and there have been both