ATC not recognising custom callsigns or tail numbers

In my system the ATC answer and out calling is OK. Also the number on my airplane. But the written callsign in the ATC-window is not able to write an E if it is called. It always writes an O!!! And this since August 2020. My airplane number is DE-GMW,
but the ATC-window shows always DO-GMW. But in time it makes me no longer angry, only laughing :joy: