Mosaic has nothing to do with it; it happens if you are sending content directly to the DAC without Mosaic in the loop at all.
dCS also has said that the code base is different between Rossini and Vivaldi so it’s not the same issue.
The basic problem is that Rossini takes too long to decide an incoming data stream is DoP rather than PCM, and rather than buffer the data while it’s figuring it out it instead discards it completely, so only DoP data received after it has determined it is DoP is played.
I posted a rather long observation of the problem in detail:
Summary:
Via USB:
Played continuously starting at Track 1:
Track 1: First part cut off
Track 2: Plays normally
Jump to Track 2:
First part cut off
Jump back to the start of Track 2:
Plays normally
Via Network:
Played continuously starting at Track 1:
Track 1: First part cut off
Track 2: First part cut off
Jump to Track 2:
First part cut off
Jump back to the start of Track 2:
First part cut off
The only workaround at present is to use playback software that can inject a half second of DoP silence before it starts sending the actual DoP datastream, meaning you cannot directly play .dsf files from a file server.