I have a 2018 with the 8 speed and the same thing is happening to me but mine is 1-2 shift. It doesn’t really slip, more like stumbles between the 1-2 shift but like yours it only happens on the first shift when the transmission is cold.
Did this help? I have acquired a rattle in the driver side of my dash but cant really tell if its coming from high or low in the dash. I notice it more at highway speeds than hitting bumps in town.