Happy to report that my CS is back from the dealer. Everything is functioning and better. Why better? See detail below.
First, the flickering gear indicator: they found a loose connection to the gear position sensor at the transmission. An easy fix.
Now the better part: it turned out the temperature sensor of the transmission was also broken apart. There was no warning or error code shown on the dash. The dealer found the issue when they were working on the gear position sensor. How is replacing the temperature sensor made the car better? After the run-in period, when I tried, she was having a hard time revving to higher rpm. Funny was I remember have to hold her back to not rev pass 4krpm when I initially have the car. I believe the sensor was broken during the run-in period, which made the computer thought the transmission is always cold (as never warmed up). As a result, the car was operating in some kind of reduced performance or protection mode. It is similar to the first 2 minute drive on a cold day before the transmission warmed up (the feeling might be easier to observe with 6MT than PDK). She is now happy to rev to 6-7krpm with ease. I will even say she came a complete different car.