Grass Valley are releasing a new patch – 10.34.11471 – and you might find if you install it you loose your Blackmagic output.
If you have the EDIUS setup manager installed it may even be prompting you to download and update.
The patch is mainly bug fixes – and does not appear to fix the colour picker bug with the 3 way cc I mentioned – but one change is that EDIUS now officially supports up-to-date Blackmagic drivers – specifically 12.4.2. Previously GV recommended you stayed on 11.5.1.
However, with the new patch it will not work with the 11.5.1 drivers so you may find you install the patch and you loose your Blackmagic output and capture. To solve this go to the Blackmagic site, download the 12.4.2 drivers – https://www.blackmagicdesign.com/uk/support/download/de2c011b1e684bf88cefefe6ff4fde21/Windows – and install them. Reboot.
Your Blackmagic output should be back.
If not, go to system settings – hardware – preview device where your Blackmagic should be listed and tick it.