Hi,
You have manually entered LX2819 as the callsign in the flight options. The system is working as intended, there is no bug that I can see. You should simply not enter the IATA code in the “ATC Callsign” field, callsigns should always use the ICAO code.
Either enter SWR2819 into the “ATC Callsign” field, or simply leave it blank and it will default to SWR2819 (Airline + Flight Number).
Best regards,