Originally Posted by dvdslw

Did you happen to have the cassette off or swap wheels? I ask because I recently bought some wheels and swapped my cassette to and from several sets before making a decision. During that process I figured out that some 11 speed wheels require an additional spacer for use with a 10 speed cassette in addition to the one spacer that came with the wheels. With one of the spacers missing the cassette was just loose enough to give me the sensation of a skip every so often, especially under power. Seems strange because all of the literature you read on 10 speed cassettes on 11 speed hubs say only one spacer is required but I needed two. May not be your issue, but you could simply see if your cassette has any play in it by rocking the large cog? Maybe the cassette locknut needs tightening?