It's buggy, but not incompletable. I've had some luck by walking back down the ramp to reset the fight and try again if things don't spawn properly or get stuck.
For the second wave (starts after turrets are destroyed), it also helps if everyone is near the middle of the turret area but not right next to the controls in the center.
On many attempts, I've had a few of the droids run into the shielded control area and then get stuck there. I think it should be inaccessible, but their pathing is weird when they spawn and they seem to ignore taunts if they are headed there. Most likely related to them not triggering at all..