in trying to debug https://issues.redhat.com/browse/DBZ-5750 i realise some logging that would be helpful is like:

scn range x to y covers logfile names: a, b, c and transactionids d,e,f

xxx rows returned from logmnr contents for the above logfile names

zzz rows sent to kafka for the above logfile names

i saw there was a suggestion on https://groups.google.com/g/debezium/c/QxpH9U83Evw/m/bCUPqapwAgAJ too:
I would suggest inside AbstractLogMinerEventProcessor#process, just after the LOGGER.debug calls that write the counters and processed entries, add the following, which will print the HEX-based transaction ids.

LOGGER.info("Active transactions are: {}", String.join(",", getTransactionsCache().keySet()));

If you want to have it print the SCNs associated with each transaction, it would be:

LOGGER.info("Active transactions are: {}", getTransactionCache().values().stream().map(T::getStartScn).map(Scn::toString).collect(Collectors.joining(",")));