something else to consider, just for the sake of completeness here. This is a big oversimplification of the system, but I think it's important to understand how the DCT trans and trans computer are trying to operate. Im not saying you dont have another, bigger issue, but sometimes the trans doesnt fucntion exactly the way we want.
The DCT transmission is two 4-speed sub-transmissions bolted together. One transmission handles even gears, the other transmission handles the odd gears. The DCT computer is always trying to guess which gear you will be selecting next and it proactively 'primes' the other sub-transmission into either the gear higher or lower than you are currently in so that the shift speed will be faster. At light throttle, at certain RPM ranges, it's a 50/50 guess which gear will be selected next. If the DCT computer chooses incorrectly, then it has to shift into another gear first before completing the shift, and this takes more time than 'normal.' The gear number on the dash changes immediately when the shift paddle is pulled, but the transmission takes a little longer to physically change gears before completing the shift.
For example: You are in 5th gear at 30% throttle just cruising. The DCT computer thinks you will be downshifting to 4th gear based on its sensor inputs, so it proactively shifts the other sub-transmission to 4th gear. However, you decide to upshift to 6th gear, so now the even gear sub-transmission has to shift out of 4th gear and move to the 6th gear position before the shift can be completed, which takes more time than expectation.
You can also test this in certain scenarios. For example, if you are hard on the brake in manual mode like on a race track, the transmission is expecting you to downshift to the next lowest gear. If you are hard on the brake and shift UP a gear, you will notice the gear change takes a little longer than if you downshifted, because the transmission has to quickly reselect another gear first.
You can start watching at 3:08 or so and watch through the end of the video to see what is happening here.