Not just engine failure/loss of power (including loss of both engines - think Air Transat A330 fuel leak) plus cargo hold fires (SAA 747 Mauritius)
We have also has seen a couple of complete electrical failures on big ETOPS twins (Just last month a LATAM 777-300 on its way to LHR)
ETOPS has been around for 30 years now with the first UK ops with Monarch London to Orlando with the 757-200 via Bangor -
Nowadays the vast majority of long haul over water operations are using large twin engined aircraft with a fair number still using older jets like the 767-300 757-200 and first generation 777 and A330's on such missions - aircraft and engines with high time cycles.
AND brand new twin jets with new advanced engine technology which has already shown some weaknesses in service due to manufacturing and or design defects (RR 787 and LEAP etc)
One has to wonder that statistically an 'event' is more likely to occur (V.V say 10-15 years ago) as twin jet usage increases, time, age and possibly unproven in-service life go on.