Mob is gone

Hello. I experienced an issue where my mobs spawn rate (Night time or digging) is suddenly very low. I mean, at night time, there's only like 5-8 mobs that appear. Even when i put off all the light source at the place and area goes dark. I tried to change the mode into peaceful and back to normal with hope the mob is back to normal but no. Could you please help? I can't play normally.

Thank you very much.