Hi Jozef.
Can you please create two log files? One should be created with List & Label Version 22, and the other with Version 31. These log files contain timestamps that allow us to directly compare both runs and identify exactly where time is being lost.
Please upload the log files via our support portal, especially if they contain sensitive or privacy-relevant data. Otherwise, you can post them here in the forum if you’re sure they don’t contain anything critical.