Only thing ive noticed is when the longbow spam the burn patches.
The fear effect drives the bots mad and they run to the end of the mission and aggro everything.
In my opinion, that is just a weakness but it's time to keep the heals ready.
: Smashing (Champion Smasher) and other melee damage, Dark Energy (simply owns: like succubus, archon morena, i hate that guy), Fire (Behemoth Overlord and others) and just Energy (Chief Stunner/Juicer). OT Fact: Archon Morena simply, took all the robots down just like 'that' (ps. i've had his mission twice, he has killed me and the bots twice. One time he only killed me in seconds).
more ot:
Ice/Psi/lethal & missiles/grenades dont seem to be a problem, depends how many you get though 
. 10+ grenades = ouch.
To be honest I find fire a strange weakness for machines :/
I guess you could say it's overheating damage but I can't think of any flame attacks that really look intense enough or last long enough in duration to really merit it.
Stuff like electricity/Energy makes sense but fire? meh
I'm not sure what the other minions are like, but my bots drop like sacks of spuds vs fire. One enemy flame thrower from a mob of even con to me will drop them to half health - from an orange will kill them all in one go; and thats a minion enemy too.
I realise they don't have inherant resistance against fire, but anyone else noticed this being a little er under balanced?
Or is it our achillies heel?