Age
Chance of second engine failing. Very remote. It has happened on several occasions to commercial jets but there are much bigger things to worry about. I can only think of 1 or 2 twin jets crashing with fatal results after losing both donks.
Fuel contam. Can happen. Very rare. There are a lot of checks to ensure fuel is of good quality. Jet engines are very forgiving and most problems from mild fuel contam are long term health issues as apposed to short term engines failing issues.
I dont know much about GE donks. FMV problems - could be. The RR engines on 330's were having huge problems too. and the rudder servos on 737's. And the flap tracks on 737's. and centre tanks also. And fairing vibrations on old 320's. The list goes on but there are monitoring process's in place and airworthiness directives and operational bulletins and modified procedures that are all designed to prevent the issue from becoming front page news. Hopefully. The airlines and plane makers are generally conservative with mechanical issues and safety.