Is your simple map flow steps inside the record A loop or outside?
Do this ,Step thru each instance of loop,and check whether maps are being dropped at some point or overwriting each time.
I assume recordA,recordB are recordists.
Initialize the recordB before loopstep,
So are you setting Loop (inarray=recordA)(outarray=recordB) and mapping the records?
please elaborate your mapping logic,so that response will be accurate.