We've found a bug with the ExcelRtdObserver code. It seems that when OnNext is called twice in quick succession the second update will sometimes be ignored.
Looking at the code I believe this is because ExcelDNA is using the current datetime, converted to an OLE automation date, as a proxy for the "new" topic value. Unfortunately DateTime.UtcNow.ToOADate will truncate to the nearest millisecond (see
) so calling it twice within the same millisecond doesn't have the desired effect.
I have experimented with using a simple incrementing counter instead (and using the same counter in ConnectData) and that seems to resolve the problem.