OLD WORLD WITH LIMITS DON’t work

Hi mojang, i have a big problem with minecraft PE.
My Old world (with limits) don’t work, Why? If i try to make it infinite work, Why?
Please, upload this issue, i take care of that world, the loading stop in “generation world” but if i make that world infinite it will work, please help me, i hope you’ ll correct this bug.
Thanks mojang.