Debugging malfunctioning ODBC

Hello,

since "a few days", I have a problem with ODBC from Linux to two of my V4R5 machines of mine. Some queries work, some don't. I can't tell since when the problem actually exists, so I can't tell which of the numerous changes in the last days might have introduced that behavior. The only thing I can tell for sure is that there have been no changes to the TCP/IP networking configuration of the client- and server machines for years.

What I could isolate about "the problem" so far is:
- It isn't related to a certain client machine.
- Failing client machines can successfully query a similarly configured (odbc.ini) V7R2 machine.
- The problem is appearing on two independent, but manually try-to-keep-configurations-synchronized server machines running V4R5.
- It's not related to a defective *SQLPKG, because I deleted dynamically created ones, and for testing purposes I set ExtendedDynamic=0 in odbc.ini — no difference.
- The failing queries also fail when done with QSECOFR => No authorization problem.
- The failing queries work when done remotely with STRSQL/CONNECT TO via DRDA.
- The failing queries work on a local STRSQL.
- Testing is done with the isql command line tool on linux, while most automatisms use Perl.
- Most working automatisms just INSERT data. These mostly seem to work. (For example, with the Spamassassin database, it's not too easily deducted if *everything* works or not. Asterisk inserting call data records fails. Asterisk querying a number to name translation table fails. Both have worked "before". Perl automatism inserting Spamassassin statistics works.)
- Re-IPLing OS/400 didn't help.

It seems that SELECTing from databases is generally affected.

With the older iseries access 7.1.0 driver, I get:

[S1000][IBM][System i Access ODBC Driver]Error in host server data stream.

With the newer ibm-iaccess 1.1.0.14, I get:

[S1000][IBM][System i Access ODBC Driver][DB2 for i5/OS]PWS0001 - function not completed successfully.


When doing INSERTs into a database which definitely works with the Perl automatism (I see new records appearing):

With the older iseries access 7.1.0 driver, I get:

[S1000][IBM][System i Access ODBC Driver][DB2 for i5/OS]SQL0901 - SQL-System Error.

With the newer ibm-iaccess 1.1.0.14, I get:

[S1000][IBM][System i Access ODBC Driver][DB2 for i5/OS]PWS0001 - function not completed successfully.


Of course, there isn't any output in the job logs of any QZDASOINIT, so I don't know what exactly is going on. I also can't find entries in QHST hinting to an error.

How can I debug on OS/400 what's going wrong here?

Thank you.

(Please refrain from advising to use current OS's. I'm a retrocomputing hobbyist.)

:wq! PoC