We did a 20 mile shake down ride yesterday and both of our new RR6s skip/slip in fifth gear. We have a Step through and a high step.  The HS has the Acera derailleur and the ST has the Altus.  The slip is worse on the HS.  I?m a bike mechanic so I check all the necessary things but it still slips.  The cassette itself has a lot of side to side play, but there is no play between the clogs.  It?s hard to tell if the chain is slipping over the teeth or if the cassette itself is slipping.  I can?t duplicate the problem on my bike stand as there needs to be a moderate amount of weight applied to the pedals.  I?ve reached out to Rad.  I?ll report back with what they said.