OAS report server sometimes does not create reports

Once in a while, users get error "REP-0178: Cannot connect to Reports Server ..." when trying to create a report. Whenever this happens, I notice that the report server java process (found by ps -ef | grep rep_) shows ORA-4020 in strace output:

$ strace -f -s 85 -e trace=write -p 3692 Process 3713 attached with 14 threads - interrupt to quit [ Process PID=3692 runs in 32 bit mode. ]
...

ORA-04020: deadlock detected while trying to lock object /Namespace0002/PKG_ACC_DATA
...

If it were from RDBMS, we would know it's a deadlock related to a library cache object, perhaps another or the current session is compiling it while this session tries to execute it. But this is from a report server, and PKG_ACC_DATA is a package in the report, not in the database (not in dba_objects). I have no solution to this problem and just kill the process. If the report server is managed by OPMN, a new report server process is immediately spawned and hung report requests are created (new files appear in reports cache directory). If not, I can manually start the report server with rwserver.sh and the problem is solved, temporarily.

Oracle support suggested increasing all kinds of capacity related params (cacheSize, initEngine,...), deleting .dat files, to no avail. I changed from in-process to standalone report server. The problem seems to occur less often. Any insight is appreciated.

Yong Huang
(Full strace output of the misbehaving report java process is shown at the bottom of http://yong321.freeshell.org/oranotes/ReportServer.txt )

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