I have found that in as far as I can remember all Sibelius projects I exported via MusicXML the standard grace notes (acciaccaturas) mostly do not play back correctly. It makes no difference whether I export compressed or not. it also makes no difference if I use the Dolet 6 plugin instead of the normal Sibelius export. What happens is that instead of the acciaccatura being played as quickly as possible as you’d expect, they take on a longer value, around the length of the main note although this can vary. What is particularly strange is that if I create just a short test project in Sibelius, the issue does not occur – only in “real” work files which typically last 20 minutes or longer. I have version 7.1.3 and have no way of knowing if the behaviour is different with the latest version, though I doubt it.
As many Dorico converts will have exported work from Sibelius, I was hoping that some might have come across the same issue, despite the fact that on a very short demo file, it seems OK.