I believe that if you kill the wrong type of mob, it should increase your mob count. As in, if you have to kill 5 more Restless spectres, and you kill a regular Spectre, then you now need to kill 6 restless spectres. So in that respect, killing the wrong mob shouldn't make it unwinnable. The problem is, the restless mobs are so difficult to kill normally, AND you have that Bristlebane-damned RNG to deal with, that killing the wrong type basically does make it unwinnable. Feels like too many things were tweeked/'fixed' at once. Hopefully a Dev can take a look and maybe rollback some of these changes. Really, for a T2 gatekeeper raid, the version from before last patch felt at a decent difficulty level.