you're using a dark palette of colors so that the color lines of the snap/grid are indistinguishable from the plain background;
also, if the current snap-to-beat setting is currently set to "Beat", "None" or else, the sub-divisions are too dense or close to show at current horizontal-zoom level, then you won't see any snap/grid, at all.
hi,
there could be reasons for that:
hth.