There is an apparent bug in the current version of Skyline 64bit (v220.127.116.1172). When exporting a report that includes precursor "Modified Sequence Full Names", sometimes a mod will be missing. Out of 321 peptides that I imported (Edit --> Insert --> Peptides) into a new document, two had this error (in both, cys carbam was missing in the heavy form; strangely it is present in the light form). Inside the attached ZIP (Modified Sequence Full Names - apparent bug.zip) is the Skyline file with the 2 peptides and the resulting exported report (transition list) with the incorrect "Modified Sequence Full Names" values (heavy rows are incorrect; light rows are correct). I didn't check if anything else is incorrect.