Does anyone know how to snap the RefDes to a common grid?
The component designator will be placed on the board with the grid that was used when making the library component. You probably do not know what that was, however all is not lost.
You can "finely tune" the position of the component designator by making your current grid much smaller.
ie click:
VIEW
GRID SIZE
(& now either choose one of the finer grids already available) or choose
CUSTOM
(& now enter a very fine grid of say 0.01mm)
now click "OK"
Now F10 will give you a very fine grid for placement of the component designator (in fact for any text & movement of any components on the board).
I hope this helps.