That being so I am stumped. However the fact that the movie fault also occurred with a streamed source may also support the idea that it is a network problem.
I have looked through the archives and this issue has been reported before. Here is a thread. You will see that internet/network issues are suggested as the cause several times. There is also an explanation of why a reboot of Bartok provides a temporarily fix if it is a network problem . However there is ultimately no clear conclusion/solution.
As this issue seems to have a repetitive and inconclusive history it may require dCS themselves to provide an explanation. Perhaps @James or @Bashcroft could chip in?