CVT transmissions really don't "shift." They use a steel belt around two pulleys which can increase/decrease their diameters, effectively changing the gear ratio. By your description, it sounds like the steel belt is slipping on the pulleys. My friend's 2016 Altima did the same thing and there was a TSB on it to replace the TCM/Valve body assembly and, if needed, the "sub-set," which is the steel belt and pulleys. This requires dropping the subframe with the engine/trans and then the transmission can be separated from the engine, torndown and repaired, which is a pretty big job, obviously. More often than not, when CVT's have issues, it usually ends up having to be rebuilt or replaced; you don't see too many wiring issues and such outside the trans.
You might want to first go to Nissan's site and do a recall search with your VIN # to see if there are any recalls or campaigns. When they do recall reimbursements for vehicle repairs that occurred prior to the issuing or notification said recall, they will cover costs regardless of whether it was done at a Nissan dealer or independent shop, however, you will need your receipt for a shop other than Nissan (the Nissan repair should be in their computer system and the costs in the servicing dealer's system...though, I would still keep the Nissan receipt, just the same). That said, it would probably be a little less headache when coming to reimbursement costs. Nissan usually doesn't repair CVT transmissions unless it is directed under a recall or campaign; they will usually go with a remanufactured unit.