Depending on chosen wash cycle washers are not always supposed to 'fill' just use enough for that cycle .
If you mean sometimes no water at all and sometimes water with same settings check hoses and valves .
make sure valves are fully open hoses securely attached and hoses from valves to washer are not pinched twisted or damaged.
Hopefully the water not getting in the washer isn't leaking all over your floor below the washer.