Unknownreported this bug
Mob leash is working at first but when the mob leaves the leashed area, leash is not working anymore and I can drag the mob forever.
For example when I set leash for 3 blocks, it's working fine but when somehow mob goes 4 blocks away from spawner, leash is not working and mob is free to go wherever he wants or players can drag them wherever they want.
There is no error or warn appearing on console.