Pretty normal - go for a hunt on these threads about the three week stall, and the three month stall and you’ll see they are both common! It will pass, just stick to your plan.
50lbs in 12 weeks is amazing, of course! No diet gets you that! Bit hard to tell cos your profile doesn’t give us your weight or goal - but rest assured, stalls are normal. I often find I lose SIZE in a stall!