UA915 IAD-CDG got out over the Atlantic and then diverted back to BOS and cancelled. See https://flightaware.com/live/flight/UAL915

united.com says the diversion and cancellation is due to "Operations." EF is no more enlightening.

0915/05MAY
P IAD/OUT 517P E00.08 EST OFF 541P
P IAD/OFF 545P
P BOS/ON 721P
P BOS/IN 724P
F BOS/ETD 1000P
N CDG/LX OPERATIONS
D FCF/DVRT BOS ENRT IAD-CDG A/OPERATIONS

SKED IAD ORIG 525P GTD C3 SHIP 2809
CDG 655A TERM 1 GTA

Anyone know the real reason. Got to believe there was a significant mechanical problem to divert to BOS rather than EWR or IAD. And of course today's UA914 CDG-IAD is now cancelled, too.