Python pub to C sub fails when using large/complex IDL

I've been struggling for a while with Python/C interoperability when using a complex topic (simpler ones work). On one Ubuntu 20.04 PC, Python to C interoperability fails (but succeeds if I comment out some of the topic fields). A clue is an OpenDDS subscriber says 'ERROR: Sedp::TypeLookupRequestReader::data_received_i - failed to take type lookup request'

I don't really know how to debug further so I've forked good old i11eperf and made branch 'complex-union' to demonstrate the problem: git clone https://github.com/smnrgrs/i11eperf.git and switch to branch 'complex-union'.

I have extended the 'ou' topic, and added a python publisher in the Python folder.

I see the following:
Python pub -> osub FAIL
Python pub -> asub FAIL
apub -> osub OK
Python pub -> Python sub OK

If the case TDTypeBd is removed from the IDL union at line 260, then interoperability works. Any suggestions would be gratefully received.

Start with the reporter's i11eperf complex-union branch and the Python folder, then inspect the extended ou topic and the IDL union around line 260. Reproduce the Python publisher to C subscriber failure and compare it with the working publisher and Python-subscriber cases. Done means identifying and fixing the interoperability failure involving TDTypeBd, with the reported combinations working.