We have seen it a few times, and assuming there is no other obvious problem, most often it is because the engine shop can not set up the C30 for an S76 installation. It is mostly in the compressor, or rather with the relationship between the compressor and turbine. Did it come after engine change or module change?
It seams to be a difficult installation to get right because of the inlet design, why I do not know. We actually had to change engine shop until we found one with S76 "experience". I do not think Rolls-Royce will admit there is a diffrence, but in the end result, there is a diffrence.
What about the stall check? it must fail that one big time if it pops during DCA check.
Like said above, this is serious, if you loose the good engine in flight and the bad one have to spool up quickly there could be a real problem.
CB