Speaking from experience, if I've done my job and not stood in the grates while the lava comes through, interrupted incinerate as soon as I can and shroud / resilience the one stack I missed, and use overcharge saber / whatever the shadow equivalent is as often as I can to get the 10% HP heal then it's time to look at the rest of the group. Most of the time it's due to placement and people ignoring the wrong mechanics.
This is particularly true if they're not familiar with the fight or managed to LoS you to avoid the low HP adds that spawn because your DPS isn't taking care of them. There are a few mechanics to the LR-5 droid that, if ignored, cause a cascade failure as the timing on the other mechanics makes things fall apart.
Example: Moving out of LoS of the healer to pick up adds (the DPS should do this), only to walk through the lava and pick up a fire dot (should not happen, or use shroud / resilience), getting a DPS drop a bubble on you at the same time you run way (should be dropping bubbles in designated areas) so that you have to run away from it but miss the incinerate (should always be in range to interrupt) and it destroys your group.
That's a very poor scenario, but I've seem parts of that happen almost every single time I've pugged this fight. I'll ask if it's anyone's first time, get no response, and see some random player die to a bubble when he drops the first one.
My favorite is when they're taking damage from the bubble and instead of moving, they take the time to type out how the healer sucks. Yeah, sure thing pal.