DCT slow to accelerate once engine is warmed up

We’ve got a 2018 Hyundai Tuscon and we’ve recently noticed that it takes a long time to get going from a stopped position once the car is warmed up. First thing in the morning when the car is cold, it drives fine, but once the temp gauge gets to 11 or 12 o’clock, accelerating from a stopped position takes an extra 1-2 seconds before the car actually moves. This feels especially scary when making turns at red lights because it looks like we are just rolling cluelessly for 2 seconds.

There are no engine lights or codes being alerted.

If I use the sport shift mode, and keep the car in first gear, the problem happens consistently. It is not starting in second gear.

In neutral, hitting the gas hard immediately shows high RPMs so I assume it’s the transmission.

We recently had an (engine) oil change at the dealer where they used some kind of "extended oil treatment" which is said to help "expand the seals and extend the life of the oil change", etc. Car has less than 20k miles.

Why would this sort of thing happen only when the car is warmed up?