It might be fixed in 188.8.131.52
At least that is what My Oracle Support says when I put in "qmxptEvlXPO2" for an ORA-00600.
As that is an internal error, MOS is the place to start for issues like that. You can always upload the corresponding trace file to get a better hit for your specific error.
Also, EXTRACTVALUE is deprecated and you should be using XMLTable or XMLQuery instead per documentation. That will probably also help you avoid the issue as well.