I am also a electrical engineer and I solved this problem by myself because at the waranty, it took like 4 to 9 weeks the repair and I decided to open the mixer up and repair by myself.
4 to 9 weeks it was a long time for a simple OLED display change and I needed the mixer for the club and my gigs.
I also run a small electronics repair shop and I have all the tools that I need for repairing electronics gears.
The problem is the display itself, you need to order a new display and change it by yourself if you are out of warranty, the procedure is very simple.
It is not the Denon fault for this issue, it is the display manufacturer fault, it was a very big number of displays that are affected by this issue.
Below this comment I have let the link with the compatible display model for the mixer that will not cause problems anymore.
Open the back of the mixer, unplug the flex cable from the board, turn the mixer face up, heat the protector glass with a hairdryier, lift the glass up, heat the problematic display with the same method, lift the display up and install the new one.
You will need some double adeshive tape to install back the new display and the protective glass above the displays.
Here is the link where you can find the display same as is in the mixer :
You cand also find the same display on Instrumentalparts, but the price is very high and the stock is 0.