Hi Tom,
The situation is strange.
It's possible that the environment variables were switched(for shadow instance) at this step.
Normally, kernel directory is always in LIBPATH. And during the upgrade, kernel in SUM folder is part of LIBPATH for shadow instance. I suppose it's /usr/sap/B1X/SUM/abap/exe for your case.
If you want to have a try, you can copy the file libSQLDBCHDB.so to the folder /usr/sap/B1X/SUM/abap/exe and repeat the step again in SUM.
Best regards,
Charles