MyBatis Batch Update Leads to PSQLException "Too many update results were returned"

I have a fairly simple implementation of a batch update via the MyBatis
functionality.

Postgres version (via RDS on Amazon Web Services): 9.6.6
JDBC driver version: 9.4

The error manifests as follows:

DataIntegrityViolationException
Root cause: BatchUpdateException
getNextException: PSQLException - Too many update results were returned.

Has anyone else run into this? I have searched far and wide for an
explanation (including here) but have not found an answer yet.

I assume this error is coming up from the JDBC driver?

The curious thing is that the update seems to work (as in database
side-effects) but it still throws an exception afterward.

Here is a fragment of the MyBatis mapper XML file for the update. The
failure can happen for as few as two or three updates, and it can succeed
with hundreds.

<update id="update" parameterType="java.util.List">
<foreach collection="list" item="item" index="index" separator=";">
UPDATE public.vid_event_timing SET mark_delete = 1 WHERE
visitor_id=#{item.vid} AND timed_node_id=#{item.timedNodeId} AND
conditional_node_id= #{item.conditionalNodeId}
</foreach>
</update>

The MyBatis/Spring configuration includes this session factory bean, set to
ExecutorType.BATCH by default.

@Bean
public SqlSessionTemplate getSqlSessionTemplate()
{
SqlSessionFactory sessionFactory = null;
try
{
sessionFactory =
getMktPersistDesignSqlSessionFactoryBean().getObject();

sessionFactory.getConfiguration().setDefaultExecutorType(ExecutorType.BATCH);
}
catch (Exception e)
{
String message = PersistLogUtil.error(logger, "Failed to create
SqlSessionTemplate");
throw new RuntimeException(message, e);
}
SqlSessionTemplate template = new
SqlSessionTemplate(sessionFactory);
return template;
}

Thanks for any help.

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