Crew sighing...
This is not meant to slag off crew, particulary not the airline in question. It probably happens in most airlines.
On a previous trip between BOM and LHR with BA, there was a particular cabin crew member that kept sighing throughout the entire flight, not to mention during the safety briefing, when he also seemed more interested in either staring out the window or down the floor.
Also during take off and landing, when you are suppose to repeat your door drill and keep an eye into the cabin (not trying to teach a lesson here), he seemed more interested in playing with his fingers and looking down the floor. I saw this as I almost sat next to him at door 5L.
Most people do have good and bad days. That's not the issue here. But, it doesn't give a very good impression and could also perhaps be a safety issue?