Hi Dane,
#1) Will this happen when you work in 8 bit or DV? Can you give that a try?
Can you also send me a copy of your system profile in XML format by saving it in Apple System Profiler? The address to send to: support[at]blackmagic-design.com
#2) The next time this happens, check what resolution your DeckLink desktop is set to? Could it somehow have reverted back to a HD resolution which will result in “snow” on an SD monitor? If so, it sounds like some sort of preferences issue. Are you running on an admin user account? Try trashing the “com.apple.systempreferences.plist” file in “~/Library/Preferences”
regards
Kristian Lam
Blackmagic Design