This issue seems to affect a small percentage of 2018 models. Service bulletin 18-097 "Clarity Fails To Charge or Finish Charging" seems to fix it for most people. This service bulletin is not automatically applied, only when the owner reports the symptom. The SB apparently does not appear when the dealer looks up by VIN which could be why the dealer didn't see anything for your car, but if you tell them to look up 18-097 then they should be able to see this SB in their system and apply the software update to your car.