Sorry that makes no sense unless your stroke has changed when you switched? If VC19 is less powerful, and/or has a lower launch angle than your present string, then it should affect all strokes the same way. I'm not familiar with Ace Big Banger, so if it's stiffer than VC19, adjust the contact angle? Obviously the strings are different, so trying to hit the same way will result in slightly different results. There will always be a bit of an adjustment with new variables. I suspect the rest of your game got a boost or at least wasn't noticeably detrimental as your "bread and butter" backhand. If it's one stroke, it's probably the execution and not the string.
There isn't a VCT19g (1.1mm) but there is a 18g (1.2mm).