@alexander.constantin SW 3.3 uses a different RTDE library than SW 3.4. Have you tried updating the files to the ones that are available in the support site? https://www.universal-robots.com/how-tos-and-faqs/how-to/ur-how-tos/real-time-data-exchange-rtde-guide-22229/
I’ve had some problems myself with this, but after using those files with SW 3.4 everything went well.