It's now being reported that "Egyptian authorities say a bomb is the most plausible reason for last weekend's deadly Russian jet crash."
Metrojet Plane Crash: Egyptian Authorities Say Bomb Is Most Plausible Scenario as Russia Halts Flights - ABC News
Also, various British media are reporting that the Egyptians say they don't have enough storage space for all the British travelers' luggage and that's why the British planes are being turned back/diverted from Sharm.