I find this species to be slower growing than the other Avicularia/Caribena that I have raised from spiderlings and their moults to be spaced out longer. I also find that it is not easy to tell if they are in pre-moult just by looking at them. Whether they are chubby, or not, doesn't seem to make much of a difference - mine are always chubby. Not eating for four days isn't really a long time. It also isn't an accurate indicator of pre-moult on it's own. They could just be full.
It's just a waiting game. I have always been a bit surprised when mine have moulted because they don't show it as obviously as other species.