To reproduce the bug, 

(works in survival mode, and creative mode)

• Get a zombie villager, and begin the process of curing the zombie villager (give it the weakness effect using a splash potion of weakness and then give it a golden apple.
• then, exit the world by pressing the save and quit button 
• and last, rejoin the world. This can cure a zombie villager very fast if this is done quickly enough.

Edit- after some more checking after submitting this bug report to see if there was already a bug report for this, I found out that this bug report is a duplicate of MCPE-29986. Sorry for the trouble and inconvenience