One solution they could try is to time positional aoes the boss throws so they go off like 0.01 seconds after the last positional update. Kind of like how they modify all dot ticks into a single 3 second server countdown.

If player position updates are out of synch, making that solution unfeasible, then any player who was in the aoe at the start of the cast should be given an extra position update request right as it goes off.

If that doesn't work, make all AOE indicators .29 seconds worth of strafing running bigger. Then at least it'll feel hard instead of unfair.