I suspect that only dCS technical staff can knowledgeably answer questions about the architecture of the processing in Rossini. However I doubt that the answer is related to this unless there is a configuration setting error as if it was to do with fundamental processing then it is likely that all of us with Gen 3 dCS DACs would suffer from it which it seems we do not.
Your further clarification of your problem has shown that I originally misunderstood it. There is no PCM/DSD switching and it occurs with .dsf files irrespective of the data “transport” used unless there is an opportunity to insert some kind of buffering or latency.
It is currently looking as if help that we may be able to provide here on the forum has been exhausted unless Andrew or James takes it up . This does now seem to be something for which dCS technical expertise is needed. It may be a hardware fault ( rare but they occur) which would not be possible to resolve online in any case and would almost certainly require liaison with your local distributor. Remember that your computer keyboard is not the only resource that you have for contacting them. Pick up the phone starting with your dealer. I do not know where you are but there is a list of international distributors also available on the main dCS website. dCS itself in the UK does have a customer service desk ( remember any time zone difference) but your local dCS contacts should be tried first as it is their responsibilty to sort the issue out.
When you find out what is that cause of the issue please post brief details here so that we can all learn.
Good luck
Pete