To lose bodyfat and maintain muscle mass, you need to eat barely enough protein and calories to have the energy to train hard, intense and heavy. If calories are too low and you don’t train heavy during a pre-contest phase, the body will adapt to the light weights by getting smaller. So eat lean, but enough to support your training intensity.
Strength loss is an obvious sign of muscle loss, so changes must be made immediately if strength takes a drastic dip. The leaner you get, strength will start to decrease, but it will be gradual and you should really suffer in the in the last few days of a contest diet.