Long Synthetic jobs fail with status 84 using OST disk storage

I'm just seeing if anyone else have or had the problem i have here when backing up a large filesystem from a client using synthetic backups writting to a HP OST plugin disk storage. Media and Master server are both windows boxes.

We have had this problem from version 7.7.3, after speaking with HP they pointed us towards being a NBU problem. After speaking with vertitas support and sending countless numbers of logs, they couldnt find why we are seeing this problem. We have a work around so we are backing up but its more me now wanting to know why we seeing this problem.

This was working fine in 7.6 until we upgrade to 7.7.3 and also upgraded the HP OST plugin to 4.0.2. We are now at version 8.1.1 and we still have the problem.

error in the backup when the sythetic runs - 

13-Jun-2018 11:55:04 - Error WriteVirtualSynth::handleEndpointMsg (pid=1952) received EXIT message from writer parent with error status=media write error(84)

13-Jun-2018 11:55:04 - Error WriteVirtualSynth::giveEndpointStatus (pid=1952) received end point error = media write error(84)

13-Jun-2018 11:55:04 - Error PlanAdmin::actionDone (pid=1952) action failed, error=media write error(84)

13-Jun-2018 11:55:23 - Error SynthJob::cleanup (pid=1952) end bpsynth with status = media write error(84)

 As anyone else come arcross this problem?