JDBC error: Unexpected packet type: 25

Hello,

I'm sometimes getting this error from the PostgreSQL JDBC driver 
(version 42.2.10):

    java.io.IOException: Unexpected packet type: 25

(Full stack trace at the end of this message).

Looks a lot like a bug or a version mismatch. The latter is unlikely 
since the driver is relatively new but the server is a bit older (11.4). 
If it were a bug I would expect more people to reproduce it, but I 
haven't found anything on google (the only result is not even about 
PostgreSQL).

For the moment I have no idea how to reproduce this error. It appears to 
happen just randomly.

I'd like to know if someone can suggest a way to gather more information 
so I can eventually turn it into reproducible steps and fill a bug report.

Also, can pg_bouncer be related?

Thanks.
Ignacio


Stack trace:

org.hibernate.TransactionException: commit failed
     at 
org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:185) 
~[hibernate-core-4.1.4.Final.jar:4.1.4.Final]

     (8 stack frames of custom application software omitted)

     at 
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) 
[?:1.8.0_191]
     at java.util.concurrent.FutureTask.run(FutureTask.java:266) 
[?:1.8.0_191]
     at 
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) 
[?:1.8.0_191]
     at 
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) 
[?:1.8.0_191]
     at java.lang.Thread.run(Thread.java:748) [?:1.8.0_191]
Caused by: org.hibernate.TransactionException: unable to commit against 
JDBC connection
     at 
org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doCommit(JdbcTransaction.java:116) 
~[hibernate-core-4.1.4.Final.jar:4.1.4.Final]
     at 
org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:178) 
~[hibernate-core-4.1.4.Final.jar:4.1.4.Final]
     ... 13 more
Caused by: org.postgresql.util.PSQLException: An I/O error occurred 
while sending to the backend.
     at 
org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:338) 
~[postgresql-42.2.10.jar:42.2.10]
     at 
org.postgresql.jdbc.PgConnection.executeTransactionCommand(PgConnection.java:829) 
~[postgresql-42.2.10.jar:42.2.10]
     at org.postgresql.jdbc.PgConnection.commit(PgConnection.java:851) 
~[postgresql-42.2.10.jar:42.2.10]
     at 
org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doCommit(JdbcTransaction.java:112) 
~[hibernate-core-4.1.4.Final.jar:4.1.4.Final]
     at 
org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:178) 
~[hibernate-core-4.1.4.Final.jar:4.1.4.Final]
     ... 13 more
Caused by: java.io.IOException: Unexpected packet type: 25
     at 
org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:2395) 
~[postgresql-42.2.10.jar:42.2.10]
     at 
org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:311) 
~[postgresql-42.2.10.jar:42.2.10]
     at 
org.postgresql.jdbc.PgConnection.executeTransactionCommand(PgConnection.java:829) 
~[postgresql-42.2.10.jar:42.2.10]
     at org.postgresql.jdbc.PgConnection.commit(PgConnection.java:851) 
~[postgresql-42.2.10.jar:42.2.10]
     at 
org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doCommit(JdbcTransaction.java:112) 
~[hibernate-core-4.1.4.Final.jar:4.1.4.Final]
     at 
org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:178) 
~[hibernate-core-4.1.4.Final.jar:4.1.4.Final]
     ... 13 more


=> select version();
                                                  version 

---------------------------------------------------------------------------------------------------------
  PostgreSQL 11.4 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 
20150623 (Red Hat 4.8.5-36), 64-bit
(1 row)