It may simply be shifter cable stretch. Do you know if the the failure of the chain movement is at the front with the chain rings or with the rear cassette-- or both? There are many terrific YouTube videos you can watch on adjusting the front and/or rear derailleur cables. You can determine if you want to attempt to do it yourself prior to your bike fitting. I'd phone ahead if you will want extra time for the shop to take a look. Have been using chain lube?