I experienced a similar situation on a Copenhagen - Heathrow flight..Everyone seated and ready for take off but a single bag was sitting in the aisle just in front of me. Cabin crew came round and assumed it was mine then walked up and down the plane asking who it belonged too..With no responses it was taken off the aircraft. Fast forward to mid flight and a passenger starts looking around the seat areas near to us..Turns out it was his with all his belongings: phone, car keys wallets etc…Not a happy person…