Hello.
I know that Vindicators named "Johnny" can attack any kind of mob, (source):
http://minecraft.gamepedia.com/Vindicator#Behavior
I just noticed that Vindicators named "Johnny" in Minecraft PE doesn't attack any mob. only the default mobs "such as players, Villagers and Iron and Snow golems."
I used to rename a spawn egg via anvil in the name of "Johnny". However nothing changes.
Also i used a name tag in it and nothing change.
You can also try it. I used it in all of difficulty.
I'm using PGN-518 (Condor P6 Pro) in Android 6.0 Operating System.
I hope you can fix this bug.
The issue relates to the spawn eggs. https://bugs.mojang.com/browse/MCPE-25244
Naming with nametag fixes this