Despawning rate is too high .

I have been playing in my survival world lately in minecraft bedrock edition and I have been seeing many mobs , as you normally would . But sometimes I see something like a pink sheep or something else and I try get a lead to lead it but it despawns in front of my eyes . I have seen things like creepers despawn seconds after spawning . They just vanish in front of me . Please fix this because a lot of mobs are despawning way to fast in my world .