jaksta ver 2.02 locks up on MacOS 10.12.6
Can you please start off by doing a full reinstall.
What you will need to do is delete the app (uninstall) from Applications instead of just reinstalling over it. Then in Finder go to the top menu and then access Go > (holding one of shift/alt/control/command) Library > Application Support > Jaksta Media Recorder and delete that folder (NOTE: doing this will erase your library file list in Jaksta, but your downloaded/converted files will remain intact). This folder and its files may already be deleted when the app is removed, but it's a good idea to double check and be thorough in case it remains and is reused when the app is reinstalled. Reboot the Mac and then do a reinstall of the latest version (https://www.jaksta.com/download/mac/jaksta-media-recorder) and it will regenerate a new copy of the deleted folder and the application files.
Start with that and we will go from there. If the problem continues can you please send a screenshot of any errors that you get and any other info you can provide.