Yes, the characters that display as red dots in the XML parser that I linked are not actually literal dots - they seem to be Unicode control characters, which (in XML 1.0) need to be treated specially. Ideally Sibelius ought to be doing this when it outputs the XML, but it might be that Sibelius is not expecting those characters to be there - possibly they are only there because the text was copied and pasted into Sibelius from some other application.
(Incidentally I am not particularly endorsing the XML parser I linked to above - it just happened to be the first hit when I did a web search for “online XML validator”. There are many others.)