Related from https://bugs.mojang.com/browse/MCPE-22331
Steps To Reproduce:
Rename a mob then re-log. You will see the name tagged mob doesn't save the name after re-logging.
This problem is not affected in the new world.
However, it is affected in the world which took over from 1.1.5 and 126.96.36.199 and earlier.
This happen randomly.(Regularity is unknown)