I do think we are being kept in the dark over some aspects of the flights. Last week my wife was on a repatriation flight from Terminal 2 LHR. Destination board showed one airport only for that flight as destination. Wife advises A/C full (320ish SLF). Over Germany SLF were advised of new destination. New destination was same Country but around 150miles away. In flight, FR24 suddenly showed 2 forward flight paths for the same aircraft - never seen that before. As soon as the flight landed (during roll out) it vanished from FR24. Doesn't exist if you search for it.
Everyone loves a good conspiracy theory, and it's not unknown for flights to be missing from FR24.
But assuming you're referring to Lufthansa/Eurowings flights from LHR to FRA and DUS, every one that has operated in the last 10 days is clearly visible on FR24 landing at its intended destination.
What was the date and flight number of your wife's phantom flight ?