Our Support team received several tickets about complications with capturing SDI from Blackmagic Decklink cards. The issue in the latest drivers from Blackmagic and it isn’t related to the Flussonic version.
We recommend using 11.5 version, we founded it very stable in our lab. Here is a link for Ubuntu/Debian package:
How to uninstall old driver and set up 11.5:
dpkg -r desktopvideo wget https://apt.flussonic.com/temp/desktopvideo_11.5a33_amd64.deb dpkg -i desktopvideo_11.5a33_amd64.deb
Some systems may require a system reboot. Have a nice day and let me know via comments if it helped you.