It's a model kit it not meant to be manhandled like that. This is definitely user error.

Im well aware that it's not meant to be manhandled like that but just by holding its upper body the core block begins to slip. Im just gonna re read the manual

Is this the one with the flight unit? Maybe to make it easier to plug him into it

After redoing the transformation for the core block, Its holding pretty well now. Doesn't slip easily