If the attack roll was a physical two ([.][.] ), all targets of the attack become missed, even if the attack total would normally hit one or more of the targets. This is called a critical miss. Resolve the attack and, immediately after resolutions, deal the attacker 1 unavoidable damage.
RB, page 9:
After Resolutions triggered effects. “After resolutions” triggered effects wait until the current action or special triggered effect has fully resolved to begin resolving itself.
If you used Flurry and rolled a critical miss with the first attack, would you deal the attacker damage before making the second attack or would you wait until after Flurry has completely resolved?