Cellphones
There have been suggestions that cellphones could contribute towards electrical systems upset. I have no idea if that is true or not, but one area I have a lot of experience (much more than any of you professional pilots) is flying in the back as SLF, especially around Asia and in China.
The point I would make (without wishing to be xenophobic) is that on many many flights I hear cell phones beeping or ringing on the last stages of approach, and some pax even carry on conversations. Some arlines make no attempt to stop this at all, and it is difficult for the CC to monitor as they are by that stage of the flight usually strapped in themselves.
Again, not putting this forward as any suggestion of cause. just noting the occurrence on Asian flights