Intermittent SDI Signal Disruptions with Driver versions 14.x and higher. 

An issue in Blackmagic Design DeckLink drivers 14.x and higher may cause recurrent SDI signal interruptions, particularly during multichannel recordings.

This behavior has been observed, especially when one or more DeckLink cards are used in an external Thunderbolt chassis.

Blackmagic Design is aware of the issue and working on a fix.

Until then, please contact ToolsOnAir Support for assistance