It's funny - my favorite mech, even with the CERPPC issues, has become the Shadow Cat with just a pair of the lightning cannons.
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Even /with/ the trouble, it's still pulling very reasonable damage numbers and doing fairly horrid things from the edges.
I think the issue is obvious for me, though, as those are the only guns on the chassis. Sometimes they're perfect... other times, you run across the dire wolf that took /seventeen/ ERPPC blasts to the right torso before someone else came along and killed it.
Not sure what's going on - but I've also had it on my end, too - occasionally, half my armor just falls off without any indication of cause (no laser sounds, no hit indicator, no PPC hit noise - it never seems to do this with ballistics), and I've eaten at least a dozen PPC blasts to the face without discernable effect.
It's definitely a thing, but I can't quantify how much of a thing. It doesn't even seem to be consistent throughout a match, though I /have/ been playing with a higher-than-normal ping (137) having moved to the european servers almost exclusively.
My usual ping on the N. American servers is under 40 - but I've had the issue to a lesser extent there, as well.