Display 1 randomly flashes black

Hello,
This has been present on my system in all of the 15 beta releases.
My main monitor, Display 1, flicks to black randomly. At least once a minute or thereabouts.
I have swapped my Display 1 about and the fault occurs on which ever monitor I set to Display 1.
Just the Display 1 screen, not the output monitors via the HD extreme 3 or the more recent Mini monitor 4K.
cheers
paul
macOS Sierra 10.12.6 (16G1212)
MacPro (Early 2009)
upgraded to…
Model identifier 5,1
Processor 2 x 2.46 Ghz 6 CoreIntel Xeon
Memory 32 GB 1066 MHz DDR3
Graphics NVIDIA GeForce GTX 1080Ti 11Gb
Mini Monitor 4K
Resolve 15.0.oB.065
This has been present on my system in all of the 15 beta releases.
My main monitor, Display 1, flicks to black randomly. At least once a minute or thereabouts.
I have swapped my Display 1 about and the fault occurs on which ever monitor I set to Display 1.
Just the Display 1 screen, not the output monitors via the HD extreme 3 or the more recent Mini monitor 4K.
cheers
paul
macOS Sierra 10.12.6 (16G1212)
MacPro (Early 2009)
upgraded to…
Model identifier 5,1
Processor 2 x 2.46 Ghz 6 CoreIntel Xeon
Memory 32 GB 1066 MHz DDR3
Graphics NVIDIA GeForce GTX 1080Ti 11Gb
Mini Monitor 4K
Resolve 15.0.oB.065